FlightGUI.FixedUpdate is expensive in saves with lots of vessels

[JonnyOThan]

I was tracking down some performance issues and I noticed that FlightGUI.FixedUpdate seems to run for every vessel in the universe (and it's in FixedUpdate so it can run twice per frame). This amounted to about 3.5ms (7.5% of the frame) in a save with 250 vessels.

[siimav]

Fixed by #151 and #154