Rewritten aircraft act method to make it framerate independant (fixes #18)

- A separate testWaypointCollisions method was created which is always
  called, even for manual control.
  This fixes the "going through a waypoint" part of #17
- In doing so, most of the numbers in AircraftType have changed units to
  amount per second, instead of amount per frame
- Added minimum speed to AircraftType so it isn't hardcoded