DeskClock: Enable backup

* Set allowBackup to true.
* Properly support device-to-device migrations (D2D) in addition to
  normal backups by switching to dataExtractionRules.
* Include the files correctly using the device-encrypted domains,
  which is where they are stored now for access in Direct Boot.

Change-Id: I1321da4b2250d083c8785386af5ba096cd0e05eb