Part of STUD-1030

This centralizes the logic for group membership, and means that we
don't need to make queries to find out whether the legacy groups names exist.

Adds xblock handler_url support to the LMS, and makes handle_ajax use
that code.

[LMS-230] [LMS-229]

I tried to make DictFieldData strict about only being used with one
block.  That effort failed ultimately, but these are reasonable changes
I made along the way.

By transparently proxying between the XModuleDescriptor and the XModule,
and between their runtimes, we can make them act as a single class, so
that we can swap in an actual XBlock instead.

- Change wording when done with peer grading ("evals" -> "assessments")
- Added ICE legend item for comment syntax
- Added conditionals to display human readable 'grader_type' to alleviate confusion
- Rename 'Show/Hide Prompt' to 'Show/Hide Question'
- Reworded grading flags
- Make ICE grading container larger to more easily allow users to read and edit larger texts
- Adjusted lots of text and word choices to make them more user friendly
- Disable previous arrow on first grader feedback and next arrow on last grader feedback
- hide ORA instructions and ICE legend when calibrating so students don't feel like they need to write feedback

Changes after comments:

- Renamed instructions element and fixed casing issue
- Renamed legend class to ice-legend
- Changing condition from != to >= to not only fix incorrect one but also catch possible weirdness
- Grammar fix in a message
- Removing grader_type conditional in HTMl to give way to the one in python
- Moving ice feedback area height styling to CSS file

More changes:

- Update ICE version
- Modifying test to reflect code change
- Adding ICE undo feature

- require confirmation when clicking Open Ended reset button (now working)
- require confirmation when submitting Open Ended essay (now working)
- disable text feedback area during calibration and let users know that they should give feedback when grading
- fixed error message typos

This reverts commit 3b29d605.

- require confirmation when clicking Open Ended reset button
- require confirmation when submitting Open Ended essay
- disable text feedback area during calibration and let users know that they should give feedback when grading
- fixed error message typos

Modified navigation tests to use MixedModulestore
Updated factories to find editable modulestore

Updated test_submitting_problems

Updated test_tabs.py

Updated test_view_authentication

Updated test_views

Updated courseware/tests/tests.py

Updated test_masquerade

Updated test_module_render

Pylint fixes

Updated video and word cloud tests

Updated course wiki tests

Updated license and open_ended tests.
One open_ended test still failing due to Mako initialization issues

Updated staticbook

Updated django_comment_client tests

Updated instructor tests

Updated instructor task tests

Updated external_auth tests

Updated course_groups

Instead, we use XModule field default values when creating an empty
XModule. Driven by this use case, we also allow for XModules to be
created in memory without being persisted to the database at all. This
necessitates a change to the Modulestore api, replacing clone_item with
create_draft and save_xmodule.

Fixes JIRA LMS-203