Support due dates for Peer Grading XModule

Merge branch 'feature/diana/close-oe-problems' of github.com:MITx/mitx into feature/diana/close-oe-problems

Conflicts:
	common/lib/xmodule/xmodule/open_ended_grading_classes/combined_open_ended_modulev1.py
	common/lib/xmodule/xmodule/peer_grading_module.py

Feature/vik/settings to xmodule

Adding in Studio Page headers and actions + help text

Refactor lettuce tests to move common stuff out of lms and cms and into common

Comment out tests that don't run correctly without prerequisites.

Fix error message provided by Instructor dashboard datadump - make it more useful

studio - adding in info icon to page intro help and making icon classes consistent in all new references

xmodule scss - resolved studio bug #191

Skip self assessment test (fails due to need for querydict for getlist t...

Skip self assessment test (fails due to need for querydict for getlist to work, but mocking querydict is painful)

Omit migrations from code coverage reports.

Also omit portal and terrain, which are used for the lettuce testing framework.

Feature/vik/improve oe ui

xmodule scss - resolved some general span styling that would override basic em or strong type styling

Soft Landing UI, Studio Nav Revamp, Sign In/Up Revisions

Flag submissions from staff grading view

Merge branch 'feature/btalbot/studio-softlanding' of github.com:MITx/mitx into feature/btalbot/studio-softlanding

Merge branch 'feature/btalbot/studio-softlanding' of github.com:MITx/mitx into feature/btalbot/studio-softlanding