Smoothing of approach track restricted to only operate if the aircraft lands with the ILS localizer still established. Slight rework to create a tdwn_index (which may be None) that can be used throughout the approach section of the code.
ILS Established phases only created if the slice is at least ten seconds long. This is to prevent transient signals appearing to capture.
Merge branch 'master' of https://github.com/FlightDataServices/FlightDataAnalyzer
Extension of process_flight data range check to cater for lower sample rate parameters