Quick backup/restore of accounts

* Workaround for (HTC bug 2275383) & (Moto bug 2226582)
* Adds checkpoints for backing up and restoring accounts
* Uses legacy Account / prefs to back up accounts - this is because
  some of this code will be reused for legacy account migration
* Unit tests of Account & LegacyConversions
* Unit tests of backup & restore
* Not done:  testing of EAS/Account Manager interface (this will require
  deeper dependency injection, to avoid the embedded calls to the Account
  Manager and other system services.)
1 file changed