FlightGear - Flight Simulator FGAddon

* Nasal/multiplayer.nas: new. Centralize all property aliasing for multiplayer.
Transmit gear/gear[*]/wow as booleans, gear/gear[*]/rollspeed-ms as floats.
Do not alias gear/gear[*]/position-norm, already transmitted by default.
* Nasal/multiplayer_local.nas: new; use the above in the local aircraft.
* Models/DH8[BCD].xml (nasal/load): load and execute multiplayer.nas in remote
aircraft.
(animations): use unaliased properties.
* q[1234]00-jsb-set.xml (sim/multiplay): delete, superseded by multiplayer.nas.
* qseries-common.xml (nasal): load multiplayer{,_local}.nas.
* Models/Cockpit/Instruments/MFD/MFD.pilot.nas,
Models/Cockpit/Instruments/ND/canvas/style.nas,
Models/Cockpit/Instruments/PFCS/PFCS.xml,
Models/Effects/ground/ground[012].xml: use unaliased properties.