It is needed for VM clone operation: we have volume.Import, but not
volume.Export - at least not yet. And doing export+import would be very
inefficient, especially on smart storage pools (like LVM).
1. Drop separate admin.vm.microphone.* calls - lets use
admin.vm.device.mic.* for this. Yes, this means microphone cannot
be attached to multiple VMs at the same time (which is regression vs
Qubes 3.2). But this is a good thing from security point of view.
2. Drop admin.backup.Restore - use standard Admin API methods
(admin.vm.Create, admin.vm.volume.Import etc)
Cc: @kalkin
