Adds a single controller for users and groups memberships and support for adding multiple projects at once (#11702).

git-svn-id: http://svn.redmine.org/redmine/trunk@13498 e93f8b46-1217-0410-a6f0-8f06a7374b81
Adds translation strings (#11702).

git-svn-id: http://svn.redmine.org/redmine/trunk@13499 e93f8b46-1217-0410-a6f0-8f06a7374b81