Takeoff and Landing pilot fix for AP Engaged check
 - didn't reference kti.index 
 - value_at_index is not great with multistates and that accuracy is not required
Takeoff and Landing Pilot now ignores '-' state
 - ensures most common value finds correct state during landing phase
most_common_value and unique_value return None or {} if all data is masked.
Merge branch 'master' of github.com:FlightDataServices/FlightDataAnalyzer