* wip(frontend): allow create cdrom disk devices

issue #973

* wip(volumes): store order number of volume

So we can sort them for change or removal

issue #973

* wip(backend): allow cdrom volumes

also store order and do not remove cdrom on machine removal

issue #973

* test(backend): test CD rom and boot order

Changed all the test with disk devices involved because
now CDs are a special case of disks.

issue #973

* feature(frontend): manage disk devices

Add, remove and change disk and CD settings

issue #973

* feature(backend): manage disk devices

Allow manage CDs and other disk devices including boot order

issue #973