WIP: Reducing query count

@wedaly, @stephensanchez: There are four tests that don't pass right now, mostly because I lobotomized the `AssessmentSerializer` to cut a lot of queries. I think I'm just going to change the contract, though I need to look a little more carefully at what's going on with feedback now. It should actually work in practice.

In any case, I put this up in case it becomes useful to run for load testing. It should substantially lower the number of queries we're doing. It won't make as dramatic an impact as @stephensanchez's work with optimizing the peer workflow query, but it should be enough to notice across most of our other queries.