Generate assessment and submission CSV data.
Added management command to upload archive of CSV data to S3
Add a scenario with unicode in all rubric strings
Add tests for unicode CSV reports
Added progress indicator to upload management command
Optimize database queries for CSV reports.
Fix issue with duplicate assessment feedback options.
Merge pull request #303 from edx/will/csv-data-2

Data upload
Add link to user documentation in the README
Merge pull request #304 from edx/will/readme-docs-link

Add link to user documentation in the README
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.
Updating tests and some simple cleanup.