Don't send RET emails after course end

Use singular getter function where only one requirement is expected

Fix program marketing page to assume less (fix 500 error on stage/prod)

Fix quality issues to get green build for master.

Video transcript preferences

Course dates web fragment for mobile apps.

Implement a course dates fragment as a web view, currently we are using
the course info page to get the course dates section by parsing the
whole html page.

LEARNER-2769

This avoids a fatal error in Django 1.9+ in most scenarios, where this
code (before this commit) will no longer result in an implicit __in
query.  This commit should be a no-op functionally for Django 1.8.

More info: https://code.djangoproject.com/ticket/25284

PLAT-1525

Make the support modal responsive

More Sass quality fixes

Merge release back to master

LEARNER-142

Adds val trancripts in outcome of get_transcripts_info and rest of flow remains the same and also add fallback  to edx-val rtanscripts for mobile accessible video endpoints.

Purpose of this, is to serve transcripts from edx-val if the requested transcripts are not found in the contentstore i.e. that's where all the transcripts are living to date.

EDUCATOR-1216

EDU-1092

Add django-simple-history back to edx-platform as a requirement.

The module is still used by (at least) edx-enterprise.

Enterprise- Version bumped to 0.51.5

Fix frontend email regex for login page.

Currently we are using Django 1.4 regex for email validation which
does not allow custom domains (e.g. eclo.solutions), fixed it with
latest Django 1.11 regex.

LEARNER-2828

YONK-776: added thread_followed and thread_unfollowed signals