Change CoordCalc to planar calculations for Performance Reasons

[TwinFan]

Current Situation / Problem
All coordination calculations use spherical calculations involving expensive trigonometrical functions.

Suggested Solution
Change to planar calculations ("flat earth"). Given that we rarely look farther than 50km this is a very fair approximation.

Benefits
Performance

[TwinFan]

In the meanwhile, a number of planar calculation functions are available. I put them in while implementing LTApt.cpp for all calculations in the airport vincinity for snap to taxiway functionality.

But existing use of trigonometrical functions has not been replaced yet.