Zen: Simplify notification policy api, add zenmode api.

 - Remove the concept of a notification policy management token
   in favor of a simple grant/deny per app.  Currently, all requests
   are immediately granted.
 - Add zen mode getter/setting, limit to apps that have been granted
   policy access.
 - Add intent for zen mode changes.
 - Public name for zen mode = "interruption filter", moved from
   NotificationListenerService to NotificationManager.
 - Add settings metadata for new DND access Settings screen.
 - Add the split sender settings for calls vs messages to the public
   Policy api.
 - This change is meant to finalize the public api, persisting
   granted app status and showing the user-visible dialog will be
   done as followups.

Bug: 18298798
Change-Id: I511be98d69939f057c0c7dc1a6dfe63d1c468193