frontend: Console PriorityComparator should be serializable

Change-Id: If1ca0640414981a01e30d2b2d44fd903c309928a
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1086244
Signed-off-by: Frantisek Kobzik <fkobzik@redhat.com>