Backup/restore notification policy.

 - Include zen + ranking config in the backup payload.
 - Owner user only for now.
 - For the most part, reuse existing policy file structure
   as the payload format, but elide items that do not survive
   across devices (info for secondary users, uids).
 - Also elide the manual zen rule, if set.
 - During restore, keep ranking info for uninstalled apps
   in purgatory until the apps exist.

Bug: 17755700
Change-Id: Iadf71a43cd0efd44fe9a0a29874d60666b6d2076
3 files changed