Autopilot: save loads of CPU cycles

Autopilot: save loads of CPU cycles

Not every xml-autopilot filter needs to run at the update rate
of the FDM. This only makes sense for the autpilot filters. Those,
who update instrument needles or environment properties for example
may run at frame rate.
This patch (thanks to ThorstenB, who is the author) forces those
filters defined in /sim/systems/autopilot into the FDM loop and those
defined in /sim/systems/property-rule into the default loop. They
show up as xml-autopilot and xml-proprules in the performance monitor