Unlink assessment models from submission models

Use anonymous student ID if available

Fix integrity error on submission under repeatable-read mode.

Add management command for populating the database with dummy records.

Show Peer Scores for Each Rubric Question

Shift the creation of the peer workflow to happen when overall
workflow is created, instead of implicitly creating it if it
doesn't exist while checking for workflow status. The problem was
that the read check happens in multiple places and AJAX requests
were hitting it at the same time. Because repeatable-read mode
prevents them from seeing each others work, a couple of threads
would find that the peer workflow did not exist and would try to
create it. This cause integrity errors because those constraints
are enforced, even if those rows aren't available to other
processes.

This should have been fixed no matter what, but it's important to
note that Django should never be run under MySQL's default
repeatable-read mode. Use read-committed. For legacy reasons,
edX's own servers are misconfigured in this respect.

[TIM-262]

TIM-287

Disable template caching

Jrbl/231 feedback on assessments

* Improved error handling and reporting

* remaining items:
 - replace submission fk w/ m2m on peerworkflowitem
 - complete move
 - initialize feedback box, grayed out
 - tests

* TODO: incomplete move, usage still in submissions api

Add performance tests for open assessment XBlock

Remove Top Metdata UI from Problem Template

TIM-270

Add display name for Studio Advanced Component menu

Minify JavaScript, remove whitespace from templates

Added pylint configuration

Add collapse/expand for grade step

Fix - General UI/Front End Clean Up

Use XBlock version with more permissive DateTime field

Clean up unused parameter to JS render functions

* removing unused icons
* adjusting spacing on response buttons/tips for smaller viewports
* revising step status width/size

Proofing UI in Studio Context