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.
Why does this return a `MobilizedBodyIndex` rather than a `MobilizedBody&`? A lot of code in this PR would be cleaner that way. And you can always ask a mobilized body for its index if you actually need it.