base

Don't back up wallpapers that we've been told not to

In addition, now that the full uncropped wallpaper image is being
backed up, we now handle that via the full-data backup path instead
of key/value.  Restore still knows about legacy data that gets
delivered via the older key/value mechanism.

This change also has the effect of removing the size limitations
around wallpaper restore acceptance.  Any size source imagery is
valid, as crop & scale are rerun in a device-appropriate way
after the restore.

Bug 25453848
Bug 25727875

Change-Id: Idc64a2eaab97a8ecc9d2b8ca5dc011f29cab324d