[mms] Allow disabling VFS via the configuration interface.
Effect transitions that actually finish within the hour
Better sanity checking for VFS existence in view.php

Coming commits should make it essentially impossible to reach this code
if VFS is off. Thus, no need for detailed error message - sanity
checking is sufficient.
Additional improved handling of installations without VFS configured
Use Turba_Object#vfsInit() to get the Horde_Vfs object to use
Don't show add file option if VFS is not available
[mms] Remove features from UI when VFS is not available or disabled.