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
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
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.
Enable un-authenticated handler urls

Updates to depend on the latest version of XBlock, which includes
support for service-to-service (thirdparty) handler urls, which aren't
authenticated with a user (unlike handler requests coming from the
xblock client-side javascript).

Co-author: Ned Batchelder <ned@edx.org>
Rename the LTIModuleDescriptor to LTIDescriptor to follow convention
Add a per-course anonymous student id

This does not yet replace the existing per-student anonymous id, but
is intended to do so in the future.

Co-author: Alexander Kryklia <kryklia@edx.org>
Co-author: Ned Batchelder <ned@edx.org>
Co-author: Oleg Marchev <oleg@edx.org>
Co-author: Valera Rozuvan <valera@edx.org>
Co-author: polesye
Make FieldDataCache use the user from scope_ids, rather than its pre-configured user

Co-author: Ned Batchelder <ned@edx.org>
Add grading functionality to LTI xmodule

Co-author: Alexander Kryklia <kryklia@edx.org>
Co-author: Ned Batchelder <ned@edx.org>
Co-author: Oleg Marchev <oleg@edx.org>
Co-author: Valera Rozuvan <valera@edx.org>
Co-author: polesye
[BLD-384]
Change video transcripts to use locators instead of locations.

Part of STUD-870
Remove code related to Pearson Testing Centers
Rebase to re-prepare PR
Add migration to remove pearson tables
Merge pull request #1791 from cpennington/rebased-lti-graded

BLD-384: Add grading to LTI module
Merge pull request #1299 from edx/zoldak/remove-pearson-code

Remove code related to Pearson Testing Centers
Removed old migration