* Update: update (or create) an addon's translation data (as some py code).
* Export PO: export an addon's translation data in a set of pot/po's files.
* Import PO: import a set of po's files to update an addon's translations.

Note: current i18n doc on wiki is completely outdated, I will try to fix this in following days.

Also a few minor edits (and add a version number to this addon!)...

Most notable difference from now on will be that all py is handled from current blender's resource dirs, no more from source dir. Better for consistency, and avoid e.g. cycles' addon to be checked twice...

Now everything should be done with ui_translate addon (which is also now fully functional again, in theory ;) ).

Notes:
* Everything is still a bit raw and sometimes hackish.
* Not every feature implemented yet.
* A bunch of cleanup is still needed.
* Doc needs to be updated too!