- Added group (we call groups "circles" so that users don't mix them up with user groups) feature to client messaging section so that messages can be sent to either all clients/resellers or to groups of clients/resellers. TODO: add circle access control so that 1) a reseller can create circles that contain only his clients, not all clients, and 2) a reseller can send messages only to his own circles instead of all circles.

Merged revisions 3049-3051,3053-3054,3058,3070,3074-3077,3082,3086-3088,3091-3092,3094-3095 from stable branch.

Merged all language files.

Fixed FS#775 - Client can choose the servers for it's client 

Added a server module for clients and a mail plugin.