Kickoff: Ability to change the order of the menu items and hide them.

I'm using the Icons-Only Task Manager and it seems to me that the
Favorites tab in kickoff is somewhat redundant, as I have added
launchers for all of my favorites in the Icons-Only Task Manager.
So in this patch I'm introducing an option to hide any menu and also
according to bug 361210 to reorganize them.

REVIEW: 128402