Admin bootstrap

Admin theme almost totally goes to Bootstrap (2.3.1).

Almost everything has been reviewed : 
- Admin theme is responsive
- News app is lighter, more dynamic
- User app is partially bootstrap-ized

Some features have not been reviewed (or reverted) because of a lack of time ... and this version have to be released ! ^^
- Permission table in the user app is almost the same than before (the same javascript too)
- Group diff has minimal modifications (I would have to redo everything again if I wanted to improve it ^^)
- Multi-selection and multi-action not yet implemented

I suggest that we could plan a second app review to implement these things when we'll release some others applications.

PS : ... Finally the Pull Request is done !!! ... Ah ? Installer ? ... Very soon, could be already finished if I didn't have this bug this morning.