Build system support for first-class Python plugins

[codebrainz]

With the new proxy plugin support in Geany and eventual update of GeanyPy to use it, we should consider adding support to the build system(s) to allow first-class Python plugins.

A few things that should be considered initially:

• GeanyPy plugins should force --enable-geanypy. Or however the dependency is best cared for.
• They should probably be compiled to .pyc files on installation, similar to GeanyPy's .py files.
• Whether we should have each their directory in $topsrcdir, or just install all the plugins found in GeanyPy's plugins directory.
• Other stuff I'm sure...

[kugel-]

I agree. Regarding the location, I would rather not place them under geanypy but instead at the top-level just like other plugins. They are also gonna need NEWS, README, etc like everyone else.

[elextr]

Agree with @kugel- the Python plugins should be top level and have the usual boilerplate. The user really should not care about what language the plugin was written in.

As for pycompiling them, IIUC the .pyc is only used if the Python being used is exactly the same version, but it doesn't hurt if it isn't, Python will just recompile it. So I don't care either way.