WIP: First pass at TIM-53, TIM-39

* TIM-39 partial: peer evaluators being shown other students' submissions and
  a rubric, and feedback in the form of radio buttions is being solicited.
  This is *mostly* plumbed through to the API.
* TIM-53 complete
* TODO: Needs tests, needs rubric_criteria refactoring

Co-authored-by: Joe Blaylock <jrbl@jrbl.org>
Updated the API so it now returns the proper points earned, and updates rows.
Fix for date serialization error, plus real total point calculation.
Adding some initial score logic into the APIs.
Merge branch 'master' into sanchez/xblock_peer_eval
Fixing the no submissions view
Cleaning up the score API and adding a few tests.
In addition to the score API cleanup, there is doc, test fixes,
and some refactoring around API use.
Some changes to the API based on review comments
Updating manage.py
Merge pull request #31 from edx/sanchez/xblock_peer_eval

Sanchez/xblock peer eval