FlightGear - Flight Simulator FGAddon

Multiplay protocol changed slightly:
- bug fix: the engines of a remote B-25 were always smoking due to abusing
float properties as booleans and comparing them with the string "true".
Send them as booleans (requires fgfs 2017.2 or newer) instead.

- Optimization: do not send engine rpm twice as engines/engine[*]/rpm and
sim/multiplay/float[4,5]; remove the latter.

- use /gear/gear[*]/wow directly in animations. Send them as generic bool
properties instead of floats.

- Transmit the caster angle of the nose wheel as a generic float.

* Models/b25.xml (nasal/load): rewrite as described above.
(nose gear): bug fix: animate using gear/gear[0]/caster-angle-deg, not
rudder-pos-norm.
* Models/main_Chrome.xml, Models/main_Default.xml (nasal/load): delete,
was never executed.