Updated setup.py
TIM-548
Bugfix: 500 error when clicking "peer assess" with no submission.
Merge pull request #306 from edx/will/update-setup-py

Updated setup.py
Quiet noisy error log message
Add AI grading architecture documentation.
Merge pull request #305 from edx/will/machine-grading-arch

Add AI grading architecture documentation.
Make peer assessment an optional step.

This also creates the AssessmentWorkflowStep model to track all
steps for new workflows. Some problems with it now:

* a lot of broken tests
* some display oddities on the peer step during (peer, self) workflows
* have not tested to see if there are concurrency issues with step
  model creation under load.
TIM-499: Database error in peer_assess handler uses variable before assignment
Merge pull request #308 from edx/will/no-open-assessments-error

Quiet noisy error log message
Merge pull request #307 from edx/will/status-details-error

TIM-548
Merge pull request #310 from edx/will/TIM-499

TIM-499: undeclared variable when logging an error
Updating tests and some simple cleanup.
Merge pull request #302 from edx/ormsbee/workflow_steps

Make peer assessment an optional step.
Supporting Peer Only configuration for ORA2