Set empty aws credentials to None.
Recover from error loading forum thread list

When a user attempts to load more threads in the forum navigation
sidebar, reset the state of the world so the user can retry, and alert
the user appropriately.
Add focus trap on forum navigation thread loading

For accessibility purposes, it is bad to allow a user to initiate
loading of additional threads in the navigation sidebar and then shift
focus away from the sidebar, only to have focus snap back when the
additional threads are loaded. Now, we trap focus on the loading element
as recommended by our accessibility consultant.

JIRA: FOR-238
changes to allow multiple choicetextresponses in one problem
Update AUTHORS
Increased timeout for element count in HTML test
revises .gitignore file to include static css directories and remnants of devstack setup
Change preview view method to use RESTful URL.

STUD-848
Separate all db ops from modulestore ops
Show error on invalid html in course handout edit + Added tests
STUD-293
BLD-524: Add missing assert in video test.
Merge pull request #1722 from edx/will/fix-html-failure

Increased timeout for element count in HTML test
Merge pull request #1680 from edx/christina/preview

Change preview view method to use RESTful URL.
Merge pull request #1719 from danielcebrian/patch-1

Update AUTHORS
Merge pull request #1333 from edx/dhm/separate_pymongo

Pull all db (mongo) functions into another file to enable easier replacement
Merge pull request #1637 from edx/feanil/aws_creds

Set empty aws credentials to None.
Test for i4x on returned pages.

STUD-941
Merge pull request #1697 from edx/christina/i4x_test

Test HTML returned from view methods for "i4X".
Merge pull request #1707 from edx/gprice/forum-thread-list-focus-trap

Add error recovery and focus trap to thread loading in forum sidebar
more granular transactions in grading [LMS-1480]

remove field_data_cache from grades.grade and grades.progress_summary

cleans grading code by adding wrappers