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.
I also think offset is inconsistent with what appears elsewhere but this seems like a particularly large interface change. "offset" is prolific in XML marker files; would the version-updating script take care of this?

We should also make a list of API changes somewhere.