Revert "Remove "Backup Calling" button from Settings UI"

Revert submission 20541028-remove_backup_calling

Reason for revert: Disables backup calling on master builds
Reverted Changes:
Iff2665829:Remove "Backup Calling" button from Settings UI
I5523465a6:Remove "Backup Calling" button from Settings UI

Change-Id: I415cfddfb365dc8911f2ded418892ceb3834ba24
10 files changed