Allow users to mention one or more friends to start a group chat
Update "Seen by" feature to work with group chat
Merge branch 'feature/group_chat' into develop
Bugfix: Unread messages in group chats cause Notification Center shows "Loading…" forever
Allow user to turn off email notifications
Bugfix: chatbox status area does not move when compose box height is changed
Bugfix: gender of user displays incorrectly in some places