Add self-restore capability to Backup/Restore sample app

The Backup/Restore sample application now provides a "restore my own
last-known-good data" button.  When it is clicked the app will run the
standard public BackupManager.requestRestore() operation.

(This was the one aspect of the public API that was not previously
exercised by the sample app.)

Change-Id: I8abcfbad4b27b35fe9fafbbb97f89bac1d7a668c
5 files changed