Several improvements and fixes in restrictions UI

Bug: 8668906 : Add string indicating that the app has opted-in
Bug: 8663558 : Fix a crash in settings when EXTRA_RESTRICTIONS_LIST is empty
               Also accept EXTRA_RESTRICTIONS_BUNDLE as a result from custom
               restrictions activity
Bug: 8653389 : Some apps show up twice in the limited user config screen
Bug: 8653915 : Jank when adding a new limited user

Change-Id: I293148000be70850f565dbddb4c942d69142ae17