Added right-click option to select MAV, ensured that waypoints get updated properly on switching MAV

Fully working waypoint interface, thoroughly tested. Active waypoint setting has to be debugged in the simulator, but works fine on real hardware

Changed waypoint list file format (old files are not compatible anymore!), added file version check, now all waypoint entries should have an entry in the waypoint list file - although qgc does not use/read the orbit_direction and param1 fields. QGC writes the value of orbit into param1 and 0 to orbit_direction (this should and will be changed later!)

Cleaned up serial link handling, eliminated double menu entries and safeguarded the link list. Did intentionally not improve the object dependency issue, will work on that on a global scope