extensions: rename 'rcextensions' into 'extensions' but provide compatibility

The 'rc' prefix is legacy.
Rename 'rcextensions' into 'extensions', updating all references.
Compatibility with the old name will be retained for a while, and removed in
a later release. Migrating is as simple as renaming a file.

front-end: fix documentation regarding theme.less file

The documentation stated that a theme.less file can be placed in the
Kallithea root directory, but this is not true. The file is expected in
kallithea/front-end to take effect.

Update the documentation and .hgignore file.

cli: add command 'kallithea-cli front-end-build'

Kallithea is under the GPL license, and we can thus only distribute any
generated code if we also ship the corresponding source.

We are moving towards a web front-end that use npm to download and compile
various open source components. The components might not be GPL, but if we
distribute any parts of their code (compiled or converted to other
representation), then we also must distribute the corresponding source under
the GPL.

It doesn't seem feasible for us to distribute the source of everything that
npm downloads and includes when we are building. It thus also doesn't seem
feasible for us to build and ship the compiled (possibly minified) front-end
code. Instead, we have to make it as smooth as possible for our users to
get up and running.

It doesn't seem feasible for us to ship or install npm. We must assume it is
available. That requirement must be documented clearly, and we must recommend
how to install npm for the most common platforms.

We could perhaps just document what manual steps to run. Kallithea doesn't
work out of the box anyway - it has to be configured and initialized. Extra
steps might not be a big problem.

Another approach is to call out to npm while pip is installing Kallithea and
download the requirements and build the files. It can be done by customizing
setuptools commands in setup.py. But: Python packaging is fragile. Even
though we only support pip, it really isn't built for things like this.
Custom output is muted and buffered and only shown if running with -v or the
command fails. And pip and setup.py can be used to build and install in so
many ways that we probably can't make it work reliably with all ways of
installing Kallithea.

The approach implemented by this commit is to add a custom cli command
'front-end-build' to run the required commands. This single user-facing
command can internally run various steps as needed. The only current
requirement is the presence of npm and an internet connection.

For now, this will just create/update style.css ... but currently probably
without any actual changes. The files created by npm (and the node_modules
directory) must *not* be a part of the release package made with 'setup.py
sdist'.

(Commit message is mostly written by Mads Kiilerich)

cli: convert 'gearbox make-rcext' in 'kallithea-cli extensions-create'

Note: 'extensions' instead of 'rcextensions' as first step to get away from
the 'rc' prefix.

less: load optional theme.less file to allow custom styles

Users can use this file to easily override the default style.
For example they can override the theme main color or the logo url.

gearbox: replace paster with something TurboGears2-ish that still works with the Pylons stack

This is a step towards moving away from the Pylons stack to TurboGears2, but
still independent of it.


Some notes from the porting - it could perhaps be the missing(?) documentation
for migrating from paster to gearbox:

Note: 'gearbox' without parameters will crash - specify '-h' to get started
testing.

Replace paster
summary = 'yada yada'
with the first line of the docstring of the Command class ... or override
get_description.

Note: All newlines in the docstring will be collapsed and mangle the long help
text.

Grouping of commands is not possible. Standard commands (for development) can't
be customized under the same name or hidden. (Like for paster, the conceptual
model also assumes that the sub-command naming is namespaced so commands from
other packages won't conflict.)

The usage help is fully automated from the declared options.

For all deprecated Commands, replace paster
hidden = True
with gearbox
deprecated = True

Note: config_file, takes_config_file, min_args and max_args are not available /
relevant.

The gearbox parser is customized by overriding get_parser - there is nothing
like paster update_parser.

Gearbox is using argparse instead of optparse ... but argparse add_argument is
mostly backwards compatible with optparse add_option.

Instead of overriding command or run as in paster, override take_action in
gearbox. The parsed arguments are passed to take_action, not available on the
command instance.

Paster BadCommand is not available and must be handled manually, terminating
with sys.exit(1).

There is no standard make-config command in gearbox.

Paster appinstall has been replaced by the somewhat different setup_app module
in gearbox. There is still no clean way to pass parameters to SetupAppCommand
and it relies on websetup and other apparently unnecessary complexity. Instead,
implement setup-db from scratch.


Minor change by Thomas De Schampheleire: add gearbox logging configuration.
Because we use logging.config.fileConfig(.inifile) during gearbox command
execution, the logging settings need to be correct and contain a block for
gearbox logging itself. Otherwise, errors in command processing are not even
visible and the command exits silently.

docs: document Kallithea customization options

Create basic documentation for the various customization options in
Kallithea. Move the rcextensions section to this new page and reword.