app: add "machine" UI
Add a new "Machine" menu, which allows to Pause/Reset/Power Down a VM.
The menu is only visible if "vm-ui" app property is set.
When the application quits, it will also send a quit action to the VM.
This is a similar behaviour/UI as qemu -display gtk.
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Acked-by: Victor Toso <victortoso@redhat.com>