Instrumentation and systems are now configureable from xml files. The two
generic configurations generic-systems.xml and generic-instrumentation.xml
configures the systems and instrumentation as it was hardcoded. You can
override the generic configurations in a similar way as you override the
autopilot configuration.
a spinning gyro.
Changed FGInstrumentMgr to inherit from FGSubsystemGroup, greatly
simplifying the (already simple) class. I should probably rename this
to FGInstrumentGroup or something similar, but not today.
Added the gyroscopic turn indicator (part of the TC).