Added the possibilty to see only one UAS at the time with the drop down menu after clearing the view

Added support for stream rate config to MAVLink inspector. Allows to configure the update rate per message

cause: check for null pointer had no effect (static memory)
solution: fill mavlink messages (and thus) message type with 0xff. this patch assumes that message ID 0xff is never used
positiv side effect: qgroundcontrol uses 2% less cpu on my machine (eeepc)