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

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

Add edx-private and sandbox req files to tox env.

Course Update emails (initial)

Delete old recurring_nudge_schedules_for_hour task

Merge release back to master

address coursegraph issue where components had the same block id but …

Adding spanish certificate template partials learner-1996