Remove ill-looking pos from dequePos

[TwinFan]

Current Situation
Aircraft seem to move back and forth, turn left/right.
Especially when different channels are combined.
Also see bug #11 .

Suggested Solution
We might need a logic to just remove an ill-looking pos from dequePos, like:

• Heading turns more than 90° but with next pos we would fly straight (<30°)
• VSI would switch between down/up, but with next pos we would keep or level

Alternative
Don't allow mixing channels for any one aircraft...but how would we decide that we need to switch channels when coverage of current channel fades and another one seems better? How would we define 'better'?

Benefit
More realistic looking landings.

Additional context
Look at this example: there is a position, which goes backward, and then we suddenly accelerate to 450+ knots:

22:53.054 LiveTraffic DEBUG LTFlightData.cpp:667/AddNewPos: DEBUG POS DATA: a/c A7C849 SimTime: 1534968806.1 - 2018-08-22 20:13:26
a/c A7C849 ppos: ( 40.790, -73.867) 54f GND_OFF {211°, 7↕︎, 0↔︎} [1534968806.1] Y: -0f Phase: 61 Final
posList:
( 40.790, -73.867) 91f GND_OFF {211°, 2↕︎, 0↔︎} [1534968795.0] <211°, 0m @ 0kt, -202ft/m>
( 40.790, -73.867) -0f GND_ON {212°, 7↕︎, 0↔︎} [1534968822.0]
posDeque:
( 40.788, -73.869) -0f GND_ON {211°, 2↕︎, 0↔︎} [1534968799.7] < 31°, 323m @ 28kt, -0ft/m>
( 40.790, -73.867) -0f GND_ON {212°, 0↕︎, 0↔︎} [1534968822.0] <212°, 1846m @ 461kt, 51ft/m>
( 40.776, -73.878) 7f GND_ON {206°, 0↕︎, 0↔︎} [1534968829.8] <204°, 340m @ 19kt, 0ft/m>
( 40.773, -73.880) 7f GND_ON {204°, 0↕︎, 0↔︎} [1534968865.4]

[TwinFan]

Solved with #57.