Optimize Subsection Grades update

TNL-5457: Performance enhancements for Discussions API.

- Default to with_responses=False, except when required.
- Clean up search call unused params.

Fix width of 'Load More' button in Discussions

Update xblock-poll dependency to v1.2.

Fix bug where new posts were not assigned a topic ID and would fail to post

Persistent Grade being saved for individual problems

* First take at forcing a subsection's grade to update when a signal is
  sent that a problem's score has changed
* Refactor signal handler connection.
* Expand bokchoy tests to cover progress page
* Add some grading unit tests

TNL-5394
TNL-5364

Pass Sailthru campaign id cookie to ecommerce

[ENT-13] Make SSO providers optionally hidden

TNL-5442

TNL-5404: Default to not requesting responses when grabbing a single thread.

Retrieve marketable MicroMasters from the catalog service

Remove duplicate-id rule for a11y discussions

Complete the LMS help link - add it to edx.org theme, adjust Sass styling for the theme and for pattern library pages

Adjusted Sass for the doc-link so that it will work in pattern library pages and also in the edx.org theme. Added the documentation link to the edx.org theme header.

We're often grabbing the metadata of a specific thread to then be able
to perform other operations, but we never need the actual responses or
comments of a thread unless we're displaying it in the normal forum
view.

This change sets a default of with_responses=False, which instructs the
comment service to not send back the responses/comments for the given
thread.  We only ask for responses in the case of rendering a single
thread or inline discussion.

Catalog-based MicroMasters need to be displayed in the LMS. However, the LMS currently retrieves all program data from the soon-to-be-retired programs service. Consuming program data exclusively from the catalog service is out of the question right now; it's too complex to confidently pull off in a week. This is a functional middle ground introduced by ECOM-5460. Cleaning up this debt is tracked by ECOM-4418.

Pa11ycrawler 1.5.0

Pattern library alerts on discussion pages

Mark DiscussionResponseEditTest.test_vote_report_endorse_after_edit as flaky

AC-577 login form contrast and invalid aria cleanup

TNL-5164

Remove placeholders in discussion new post form

Merge release back to master

Release Candidate rc/2016-09-06

TNL-4945 – Prioritize Library defaults over the fields coming from parent blocks.

TNL-4647