CSV Reporting of Shopping Cart Purchases, with tests

squashing to one commit to make cherry-picking by feature possible
Add feature to do auto signup with external auth
This adds a feature flag: AUTH_USE_MIT_CERTIFICATES_IMMEDIATE_SIGNUP
that does an automatic signup of users if they are using external authentcation.
Fixed PEP8 and indentation issues
Added tests for signup skipping
Corrected CMS tests so that one is passing, added external_auth to cms apps
Several pylint fixes and bad super call
Changed unit identifier to be readonly, not disabled

STUD-863
Added refund datetime info to Orders, OrderItems

Finance would like to have info about the date any given refund is requested.

This commit adds a refund_requested_time field to OrderItem and a refund_time to Order.

When a user *requests* a refund, the refund_requested_time field on OrderItem is updated; when a user actually *receives* their refund, the refund_time on Order is updated.

Note that only the refund_requested_teim field is actually used right now; later on, when we're able to actually automate the process of actually giving users refunds, we will start usings Order's refund_time field.
Removing external_auth addition to cms, and skipping test
Studio: correcting hiding state of notification UI for < IE9
STUD-815
Merge pull request #1773 from edx/andy/unitidentifier

Changed unit identifier to be readonly, not disabled
Disabled video caption tests that failed in master
Merge pull request #1786 from edx/will/disable-caption-test

Disabled video caption tests that failed in master
Merge pull request #1779 from edx/talbs/fix-studio-notificationsie

Studio: FIX - correcting hiding state of notification UI for < IE9
Studio: adding basic italicize text styling into xmodule/block preview UI
STUD-963
Merge pull request #1778 from edx/talbs/studio-fix-italics

Studio: FIX - Italicize in xmodule/block previews
Disabled another video test that failed in master
Merge pull request #1788 from edx/will/disable-caption-test-2

Disabled another video test that failed in master
Refactor keypress activation for forum buttons

This removes the use of the space key to activate buttons, which is not
expected behavior.
Improve accessibility of inline discussions

The show/hide toggle now properly acts like a button, and focus is now
trapped on the loading element for both the show/hide action and loading
of a new page.
Merge pull request #1685 from edx/jbau/shopping-cart/report

CSV Reporting of Shopping Cart Purchases, with tests