Added method to specify which layout to reload

NOTE: With this method, it is now possible to specify loading an alternative
      layout. The layout will still be passed through the repair method, in
      order to ensure that it is compatible with the current icon layout
      constraints.
Actually display the stale file alert
Removed need to respring after showing stale file alert
Renamed directory to reflect purpose (PostInstall -> extrainst_)
Changed how stale file is handled

NOTE: The stale file is now not applied until the user says to do so.
Renamed file to reflect contained class (ISStaleFileAlertItem)
Simplified wording of stale file alert
Must call original implementation to dismiss the alert item
Override "Reset Home Screen Layout" to allow layout selection

NOTE: Users can now choose between using the usual "factory defaults"
      or their current Safe Mode layout.