Add UI styling for course staff, including collapse/expand.
Cache student item when retrieving submission and student item.
Protect against invalid cache key exceptions.
Update test suite to clear cache between tests.
Add composite index for AssessmentWorkflow student item fields

Inputs in any user-editable text box that are too large will be rejected
without an AJAX call.

Inputs delivered via Python to the API which are too large will be
rejected with an approriate API error.

TODO:
 * @talbs .message__content is styled very badly everywhere
 * Sizes are way too big, currently defaulting to 1MB for API and 256KB
   for js
 * Sizes are configured in too many places, when they should come in via
   settings or something

One of many small pull requests that are going to come for [TIM-279].

This is what will be called by the LMS when querying the submissions
app for the raw scores of a student in a particular course.

[TIM-232]

Validate assessments are specified in the order: peer, then self.
Update XBlock date fields to use scope.settings and be named "start" / "due"
Add validation to workbench scenario parsing.
Resolve unspecified dates.
Use resolved dates to determine whether problem/submission/assessments are open or closed.

Wiring all the peer queue into place

Updating based on rebase to fix tests

Implement self assessment api

[TIM-202]

In addition to the score API cleanup, there is doc, test fixes,
and some refactoring around API use.

More documentation, repr, corner case testing, and proper validation