(other than "none") is "spin", which must be tied to a property giving
a value in RPM. This gets the DC-3 propellers turning. The next type
will be "rotation", which will allow the flaps, elevators, ailerons,
and rudders to move (and even gear, eventually). Later, I'll add
"shift" for sliding things around, and will figure something out for
blinking lights.
the XML file, including the path to the 3D file.
This change obsoletes the existing /sim/model/*-offset-deg and
/sim/model/*-offset-m properties in the main property tree, and
replaces them with /offsets/*-deg and /offsets/*-m in the model
property file. The /path property in the model XML file is relative
to the XML file's location rather than FG_ROOT.
