secure-cookies: Allow to use secure HTTPS cookies (Django setting)

Cf https://docs.djangoproject.com/en/1.4/ref/settings/#std:setting-SESSION_COOKIE_SECURE
keep large answers from appearing (TNL-441)
Change some text when in professional ed flow

ECOM-96
Updated help link and content of container page
adjusting style for professional educationand verification status
Don't set 'download_video' field on importing video from xml until explicitly set
TNL-324
update video module to always set download_video field on export
Added tests for unparsable matlab grader response.

TNL-388
If matlab grader sent unparsable response, show error message
instead of trying to render the response.

TNL-388
add simple help-modal-test
Allow SSL enforcement for OAuth2 provider to be configurable
Return OpenID Connect user name from user profile.
Content experiments update

comments from Anant
Merge pull request #5295 from edx/adam/add-simple-help-modal-test

add simple help-modal-test
Merge pull request #5318 from edx/markhoeber-doc936

Content experiments update
Merge pull request #5315 from rocha/fix-fullname-in-oauth2-handler

Return OpenID Connect user name from user profile.
Use default locale to OpenID profile claims.

If the user has not selected a default locale, then return the default one.
fix 404s when students access group-less threads in cohorted topics

TNL-444
adjusting ID verified status to be just verified status
capa custom response support for decimal grades