Certificate report improvements

LMS: Show Enrollment Type on Dashboard

These files are not being used.

Show error page templates on Studio

Reorganize information in CONTRIBUTING.rst, link to ReadTheDocs

Remove email field from CS client user object

Markhoeber/documentation/doc 332

To remove XML info that’s in course staff doc now.

doc-332

LMS-1071

Sarina/050514 language update

ORA2 release-2014-05-05T12.00

Update the software secure result call back by correcting the typo

LMS-2516

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

/request_cert AJAX endpoint

* 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>

* 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.

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'

Expose "enabled" checkbox in Embargo admin

STUD-1558

This requires cs_comments_service commit 1d50176.

Fixed link to docs.edx.org in readme

Parameter from_email to send_mail() should be string

Update drag and drop documentation

Fixes firefox image hidden overflow bug.