Some cleanups and fixes, and use new "progressbar" api for main translation operators (which can be rather long), thanks Gaia! :)

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Note: current i18n doc on wiki is completely outdated, I will try to fix this in following days.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

Mark ui_translate as broken for this release, new code is nearly ready, but it's too late for such huge changes now.

make addons blender versions consistent

Fix for another dummy mistake (was preventing RNA label to show up the first time, because of context overwriting...)

This is the py addon to use for embeded Blender ui translation. It can edit various UI elements' messages and tips, save the changes to the relevant po, "compile" a new mo placed into user's datafiles dir, and erase that same files (to get back "official" translations).

Notes:
* Still work in progress. Most likely some remaning bugs (even though it works quite well for me)...
* All UI elements in Blender aren't translatable this way (e.g. panel labels just don't react to right mouse clicks currently...)
* RTL languages won't work as well as others, still have to implement some kind of revert-RTL process...
* Having a nicer way than editing user_settings.py in modules/bl_i18n_utils to set up needed parameters is mandatory! Will try to use some kind of user preferences in user's config dir.

And a whole doc to write! :/