First pass at ARIA. Video player buttons announce themselves as button when used with a screen reader

Refactor upload tests and add locked asset tests for registered user

Create management command to edit course's tabs

Conflicts:
	lms/djangoapps/instructor/views/instructor_dashboard.py

Fix run single test example

New XML infrastructure for XBlocks

We aren't ready to use XBlock.load_class, there are duplicate entry point names, and simply choosing the first one leads to unpredictability.

Just works on the tabs list in mongo, nothing
deeper than that.
Added implementation functions in tabs.py,
providing a first step for some future
GUI editor.

All video controls have a full outline when receiving focus

make ENABLE_SHOPPING_CART truly optional

course_about was throwing 500s if ENABLE_SHOPPING_CART=False

Fix course enrollment count in instructor dashboard

Add .noseids to .gitignore, but first organize it.

Fix AN-115

First caption does not display outline on initial mouseover.

Streamling, test, and fix issues with image uploading

old pr 271 comment fixups

Improvements in forums nav sidebar

Clean up open ended problems view and fix error.