pytype: add Python type annotations where necessary to guide pytype

Mute pytype warnings:

File "kallithea/lib/auth.py", line 142, in _cached_perms_data: No attribute 'DEFAULT_USER_ID' on module 'kallithea' [module-attr]
File "kallithea/lib/vcs/backends/base.py", line 73, in ...: No attribute '...' on BaseRepository [attribute-error]
File "kallithea/lib/vcs/backends/base.py", line 405, in ...: No attribute '...' on BaseChangeset [attribute-error]
File "kallithea/tests/api/api_base.py", line 2397, in test_api_get_changeset: No attribute 'TEST_REVISION' on _BaseTestApi [attribute-error]
File "kallithea/tests/api/api_base.py", line 2445, in test_api_get_pullrequest: No attribute 'TEST_PR_DST' on _BaseTestApi [attribute-error]
File "kallithea/tests/api/api_base.py", line 2445, in test_api_get_pullrequest: No attribute 'TEST_PR_SRC' on _BaseTestApi [attribute-error]
File "kallithea/tests/api/api_base.py", line 2467, in test_api_get_pullrequest: No attribute 'TEST_PR_REVISIONS' on _BaseTestApi [attribute-error]
File "kallithea/tests/api/api_base.py", line 67, in api_call: No attribute 'app' on _BaseTestApi [attribute-error]
File "kallithea/tests/base.py", line 154, in log_user: No attribute 'app' on TestController [attribute-error]
File "kallithea/tests/base.py", line 169, in _get_logged_user: No attribute '_logged_username' on TestController [attribute-error]

celery: drop kallithea.CELERY_EAGER - it is more spot-on to look directly at task_always_eager

The global flag was set as a side effect in the make_app function. That's not
pretty.

routing: move ADMIN_PREFIX constant from routing to top level kallithea module

Perhaps not the ideal place, but that is how we handle somewhat similar data.
This avoids an unfortunate dependency from the model to routing.

db: move URL_SEP constant from db to top level kallithea module

URL_SEP is used in several places - having it in the db module is too high
level.

__init__ might not be the best place for this, but it does no harm to the
dependencies graph to place constants there.

celery: refactor initialization - replace global CELERY_ON flag with CELERY_APP with the actual celery app that it indicates

Prepare for fixing how 193138922d56 broke celery due to magic dependencies on
initialization of global state at import time.

py3: switch to use Python 3 interpreter, temporarily leaving many things very broken until they have been migrated/fixed in a reviewable way

Bump Mercurial minimum version to 5.2 - the first version that claim stable py3
support.

backend: replace Pylons with TurboGears2

Replace the no-longer-supported Pylons application framework by TurboGears2
which is largely compatible/similar to Pylons.
Some interesting history is described at:
https://en.wikipedia.org/wiki/TurboGears

Changes by Dominik Ruf:
- fix sql config in test.ini

Changes by Thomas De Schampheleire:
- set-up of test suite
- tests: 'fix' repo archival test failure
Between Pylons and TurboGears2, there seems to be a small difference in the
headers sent for repository archive files, related to character encoding.
It is assumed that this difference is not important, and that the test
should just align with reality.
- remove need to import helpers/app_globals in lib
TurboGears2 by default expects helpers and app_globals to be available
in lib. For this reason kallithea/lib/__init__.py was originally changed
to include those files. However, this triggered several types of
circular import problems. If module A imported something from lib (e.g.
lib.annotate), and lib.helpers imported (possibly indirectly) module A,
then there was a circular import. Fix this by overruling the relevant
method of tg AppConfig, which is also hinted in the TurboGears2 code.
Hereby, the include of something from lib does not automatically import
helpers, greatly reducing the chances of circular import problems.
- make sure HTTP error '400' uses the custom error pages
TurboGears2 does not by default handle HTTP status code
'400 (Bad Request)' via the custom error page handling, causing a
standard non-styled error page.
- disable transaction manager
Kallithea currently handles its own transactions and does not need the
TurboGears2 transaction manager. However, TurboGears2 tries to enable it
by default and fails, throwing an error during application initialization.
The error itself seemed to be harmless for normal application functioning,
but was nevertheless confusing.
- add backlash as required dependency: backlash is meant as the WebError
replacement in TurboGears2 (originally WebError is part of Pylons). When
debug==true, it provides an interactive debugger in the browser. When
debug==false, backlash is necessary to show backtraces on the console.
- misc fixes

tg: minimize future diff by some mocking and replacing some pylons imports with tg

No actual tg dependency yet, just a temporary hack faking tg as an alias for
pylons.

Based on work by Alessandro Molina.

Turbogears2 migration: remove some references to Pylons in comments

In order to minimize the diff of the actual Turbogears2 migration, this
commit already removes certain unnecessary references to Pylons from the
Kallithea source base.
Places where the reference to Pylons is important are still kept for now, as
well as references in kallithea/config where many changes are made for
Turbogears2 anyway.

auth: cleanup of EXTERN_TYPE_INTERNAL

Don't set it in top level namespace - it is a weak link between the database
and the actual implementation. Don't make it more than that.

Don't hardcode in that many places that 'internal' is the default - just call
it DEFAULT_AUTH_TYPE.

Don't use it for extern_name - it is only intended for use as extern_type.

Remove unused uses.

lib: simplify version; drop get_current_revision - it was run every time on import time - we don't want that

This functionality was already not in use with the version numbers we use. I
also doubt it is possible to have version numbers where it worked - it seems
like there might have been some regression that nobody noticed. Dropping it
will thus not really lose any actual functionality.

If we want to include the revision number in the version (for browser cache
invalidation) then we should do it in a different way. Perhaps writing it to
some file from setup.py .

db: remove SQLAlchemy Migrate support

The DbMigrateVersion table will be removed in a later changeset.

db: drop RhodeCode compatibility (database rebranding etc.)

To migrate from RhodeCode, users will have to first migrate to
Kallithea 0.3.2.

release: set version number to 0.2.9 to hint that it is a 0.3 rc

I don't trust the rc numbering system in kallithea/__init__.py and how it
interacts with pip versioning.

cleanup: make module self-naming consistent

The self naming is quite pointless ... but at least make it right.

db: tweak configuration of branding self references

For RhodeCode compatibility:
echo "BRAND='rhodecode'" > kallithea/brand.py

SETTINGS_PREFIX for identifiers (e.g., db table names) incl. project's name.

kallithea.SETTINGS_PREFIX is a variable string used as a prefix for specific
external identifiers, such as database table names (and likely later form
fields), so that the name of the project need not necessarily be encoded into
data.

This setting is configurable so that compatibility with old, similar
databases can be maintained at the users' request.

Correct licensing information in individual files.

The top-level license file is now LICENSE.md.

Also, in various places where there should have been joint copyright holders
listed, a single copyright holder was listed. It does not appear easy to add
a link to a large list of copyright holders in these places, so it simply
refers to the fact that various authors hold copyright.

In future, if an easy method is discovered to link to a list from those
places, we should do so.

Finally, text is added to LICENSE.md to point to where the full list of
copyright holders is, and that Kallithea as a whole is GPLv3'd.

Second step in two-part process to rename directories.
This is the actual directory rename.