Save Sampler State to Sharable File

[baconpaul]

This subsumes issues #464 #466 #465

Basically the SC description is a stream of the engine which contains a stream of the parts. That's what we push into the daw. Fine.

We alsy want sharable states. Those have four forms which is the outer product of

1. Save current part only
2. Save all parts (Multi)

with

1. Save just the JSON vs
2. Collect the samples, change sample paths to relative, and save as a compound object (a zip file probably)

So the entire set of activities around those features, including UI, format, etc... is consolidated now into this issue.