TIM 386 -- Wire up UI messages

Wires up the UI messages through:
--Six message HTML templates which accept contexts to render messages for each potential evaluation step
--Changes to the JavaScript to update the Message portion of the XBlock both 1) automatically and 2) after the Peer portion of the XBlock updates.  This solves our race condition with a local field in the XBlock (no_peers) which transmits whether the Peer was able to grab a Peer submission.
--Changes to the Base HTML template to enable message display
--an XBlock mixin to determine which HTML template to render
--A method in the XBlock which returns all status details on all assessments.  This was primarily so that if we want to modify any of the messages (at any time) we will only need to modify the template, and will not need to add additional changes to add additional granularity.
--Two typo mistakes in comments.