Add backup/restore REST API methods

Add stubs (dummy implementations)
for backup/restore REST API methods

Change-Id: Ib0deea3e183bf6a94cdebf3df19dd7151ee3079b
Partially implements blueprint: backup-restore-api
(WIP) Add backup manager

Change-Id: I44f575b0e87f1ba19113ad5267073ae9edddf0b5