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: move send_email task to a better home in notification model

Avoid bundling everything from many different layers in one big task library.

This is more feasible now when we don't need kallithea.CELERY_APP set at import
time.

celery: move repo create tasks to repo model - that's where it belongs

Avoid bundling everything from many different layers in one big task library.

This is more feasible now when we don't need kallithea.CELERY_APP set at import
time.

The whole thing about model classes and instantiation is just trouble - we will
get rid of that soon.

celery: move Whoosh indexing task to whoosh library where it belongs

Avoid bundling everything from many different layers in one big task library.

This is more feasible now when we don't need kallithea.CELERY_APP set at import
time.

model: simplify how get_commits_stats task group on author

Avoid using the caching h.person . We want to get rid of the model
dependency on helpers.

The stats are persisted, and any temporary incorrectness in the long term
cached h.person will thus remain forever. It is thus arguably better to avoid
using it in this place.

get_commits_stats is also a long running task, so speed is not *that* critical.
And generally, processing commits in order will have a lot of the same
committers, so a local cache will have a good hit rate.

(Alternatively, h.person could perhaps be in user model ... but that's not how
it is now.)

controllers: move controllers base class from lib/base to controllers

TG quickstart put it in lib/base.py , but it fits better on the controllers
layer as a base there.

The contributing docs were a bit ahead of time ... but with a typo.

docs: describe, visualize, and verify internal code structure and layering

Try to describe something that isn't entirely there yet.

deps.py will help track and minimize violations through checks and
visualization in deps.svg .