Splitting up the "Big Proposal" on layering and quality into separate proposals: layering and quality

After the "big proposal" on layering and quality, the discussions seemed to
agree that:


- Overall, it's good.
- We need a few more knobs, or slightly different knobs, especially around
the spatial/temporal bias.
- We need to flesh out the feedback mechanism to JS
- We should make a separate proposals for layering, quality, and perhaps
the JS feedback mechanism


So, here's what I'm going to do:
1.  Post a proposal for layering which is separate from quality.
2.  Post a proposal for quality which is separate from layering and
incorporates feedback for the spatial/temporal bias.
3.  Leave the JS feedback TBD :).

I hope you like the imminent proposals.