OF-2398: Admin console: add visual indication of MUC room being locked
MUC rooms can be 'locked', which typically occurs when they are initially being created and configured. When a MUC room is 'locked', it cannot be entered by users.
The Openfire admin console should make it possible for an administrator to see if a room is locked.
This commit replaces the value in the 'users' column on the room summary page with a 'lock' icon, and displays a warning on the room settings page, when the room is locked.
OF-2385: Do not load shared groups when they're not supported
Group providers define if they support group sharing. If this is not supported, Openfire's GroupManager should not attempt to load shared groups.
All providers that ship with Openfire do support this feature. This change would only benefit future or third party providers.
