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.
@aseth1 

> If a RigidFrame is mobilized body and a fixed transform can you please explain to me what a FixedFrame is?

A RigidFrame is NOT a mobilized body.  A rigid frame knows its mobilized body and transform on the mobilized body.

A FixedFrame is a RigidFrame (thus still constant transform on a mobilized body), specifically defined relative to any other reference RigidFrame.  

> I am only advocating for a slightly stricter definition that RigidFrame is the fundamental rigid element in OpenSim and thus the incarnation of a MobilizedBody

We fundamentally disagree on this.  A RigidFrame is NOT the OpenSim incarnation of a MobilizedBody.

A Body is a RigidFrame defined by itself and the Joints that connect it to the articulating system.