Expanded logic of how classifiers are assigned to AIGradingWorkflows.

Unify Exception Handling and Logging policies

Will/use real classifiers when simulating errors

Will/example based test course

AI concurrency/perf tests

Clean up logging in peer and self assessment mixins

Remove cache key versioning

Will/vagrant like prod

Fixed reschedule click handler

Bugfix!  Commit the AIGradingWorkflow model before scheduling a grading task.

Will/reschedule task priority

Update ddt to 0.8.0

* gunicorn
* nginx
* mysql
* memcached
* celery flower
* upstart

Set file encoding for Python interpreter to fix a test failure in the Vagrant VM.
Configure Vagrant log files to go to logs/vagrant.

Catch a peer API workflow exception

Information about AI workflows gets sent to datadog

Update perf test to load steps in parallel.
Update perf test to hit end-points whether they're ready or not
Generalize problem fixtures, select rubric options at random
Add continued assessment to peer step
Add example-based grading to perf test
Update test course and readme

Conflicts:
	apps/openassessment/workflow/api.py
	apps/openassessment/workflow/test/test_api.py
	apps/openassessment/xblock/static/js/openassessment.min.js

Gracefully handle self-assessment with no submission.

Gracefully handle peer assessing before submitting a response

Sanchez/fix grade mixin for ai

Split up create and get for Student Training Workflows

Will/set training task priority