Do not show "View in Studio" links for child verticals of verticals.

STUD-1558
Expose "enabled" checkbox in Embargo admin
pep8/pylint cleanup
Merge pull request #3580 from edx/sarina/show-enabled-checkbox

Expose "enabled" checkbox in Embargo admin
Adds very basic about page style to ul, ol and dl

About pages need basic support for lists since professors often want to display lists or 'definitions'
Merge pull request #3435 from caesar2164/giulio/ul-ol-basic-style

Adds very basic about page style to ul, ol and dl
Certificates: URL endpoint for cert gen

* API endpoint for certificate generation, an authenticated  post with course
  id requests that grading be carried out and a cert generated for
  request.user in that course, using the usual grading and certificate
  machinery (ie, it does not imply whitelisting, though whitelists and
  blacklists will be respected)
  - Logs each request as it comes in
  - Calls xq.add_cert() and consequently, does grading synchronously on
    this app host and then queues request for certificate agent.
  - example usage:
    ```
    curl --data "student_id=9999&course_id=Stanford/2013/Some_Class" http://127.0.0.1:8000/request_certificate
    ```

* Studio advanced setting added, "certificates_show_before_end", which
  determines whether a course should permit certificates to be downloadable
  by students before the coures's end date has passed.
  - Modifications to dashboard view and templates to allow display of
    certificate download links before course has ended.
    (XXX: may declare failing students as failing before the course has ended.)
  - To test, turn the setting on in a course which hasn't ended yet, and
    force certificate generation for a student, then check their
    dashboard.
Certificates: 'Grade Me' YAML file

* Sample HTML and javascript to show how you might integrate the
  /request_certificate endpoint into a course.

Co-authored-by: Joe Blaylock <jrbl@jrbl.org>
Merge pull request #2533 from edx/jrbl/certs_request_cert_endpoint

/request_cert AJAX endpoint
Merge pull request #3576 from edx/christina/view-studio-bug

Do not show "View in Studio" links for child verticals of verticals.
Convert lettuce video tests specifically using youtube stub