Detect empty device accounts.

This queries groups and settings to find device accounts in the case that
there are no raw_contacts associated with an account

Test:
Manual test
* Remove all device contacts from LG G5
* relaunch app
* verify that "Device" doesn't show in nav drawer
* press FAB
* verify that "Device" does show in account picker in the editor
* add the contact to the device account
* verify that "Device" now shows in the nav drawer

Bug 30867780
Change-Id: I12bba7a1b5a5f37048517264cb82a599197f6d05