Implement client side logic for handling expiration of sessions.

XXX this requires logic also in the backend to return a proper data structure
to support expiration.
initial fix in order to split translation file and allow full text customization
implemented footer configurability https://github.com/globaleaks/GlobaLeaks/issues/576
Merge remote-tracking branch 'origin/feature/translations_customization' into premerge/devel

Conflicts:
	Gruntfile.js