The new mp protocol allows:
- livery support
- damage to wing, propeller and turbine
- propeller disk
- presence and position of doors (all six of them).
* PC6-B2H4-set.xml (sim/multiplay/generic): new; alias some properties
and transmit them over mp. Note: we use booleans from version 2017.2.
* Models/PC6-B2H4.xml (nasal/load): new; receive the generic properties and
alias them to the ones used for animations. Also add livery support.
