Matt ayman frames

Redo of the merge of Frame, RigidFrame, FixedFrame, Station and Marker ModelComponents along with code to convert Marker to new format for serialization/deserialization and inclusion of FrameSet in model.
@sherm1 @msdemers @aseth1 or @chrisdembia Please review and let us know your feedback.
It's a good question. I am not sure why we need to get an OpenSim::Body from a RigidFrame. It 1) might not benecessary and 2) not always possible.  A FixedFrame could have a service to provide its root (Anchor) RigidFrame (which it is already doing to supply getAnchorTransform).

If can always get a handle to a RigidFrame and you can apply Forces or connect Joints to them, why do you need to get a handle to an OpenSim::Body?  My hope was that we would make everything that connects and uses a Body for anchoring could be upgraded to a RigidFrame. In which case the need to get Body specifically is no longer relevant, or is it?