frontend: Client shortcuts for VNC sessions

This patch
 - adds client shortcut mapping for toggling fullscreen and releasing
   cursor to VNC descriptor file (.vv file),
 - sets VNC client window name in the same way SPICE does it, i.e.:
     (<vm name>:<display number> - <release cursor shortcut>)

Change-Id: Ic292e62743debf3c7af11497b74c607ebbaa98bb
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>
Bug-Url: https://bugzilla.redhat.com/1083766