Add tests for submission step rendering
Add unavailable state for submission step

Refactor save status context

Refactor date format
Update the due date parsing script to display properly.

Conflicts:
	apps/openassessment/xblock/peer_assessment_mixin.py
	apps/openassessment/xblock/self_assessment_mixin.py
Merge pull request #260 from edx/will/submission-unavailable-2

Submission step unavailable and Display Timezone UTC
Use UTC when finding the current time
Merge pull request #262 from edx/will/utc-now

Use UTC when finding the current time
Review error messages and UI text
Edit error messages in .py files
Corrected tiny typo in models.py
Revise UI and error message text in .js files
Updated "Could not contact server" error messages
UI and error message text updates