Added flag for indicating a model *with* changes.
Added flag for indicating a model *with* changes.

This might be an unnecessary optimization. The existing code had an opportunity
to perform to UPDATE statements to the database. This will just do a single
call to `.save()` for the UserPreferences model.

CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend,CCI-MOC/GUI-Frontend