make embargo template theme-able

Use "Stanford-style" theming to enable you to put your own embargo
notice up.
missing themed embargo page fails safely to unthemed
Convert CAPA inputtype statuses from strings to objects, in order to
simplify css class management and internationalization of status strings
(potentially) displayed to the user.
Add SHOW_PROGRESS_SUCCESS_BUTTON feature

Show a button at the top of lms/templates/courseware/progress.html if the
lowest nonzero grade cutoff has been reached. Introduce two settings:
PROGRESS_SUCCESS_BUTTON_URL is the href of that button (the course id is
appended); PROGRESS_SUCCESS_BUTTON_TEXT is the text, defaults to
"Download your certificate"
Make the SHOW_PROGRESS_SUCCESS_BUTTON feature more flexible

The button text default is now in the template and i18n-able, a
PROGRESS_SUCCESS_BUTTON_TEXT_OVERRIDE option is offered in settings.
The button url now uses string formatting.
Updating ORA2 requirements for patch fix
Explicitly declare `tags` in dog stats increment calls
Fix source editor for the case of no CodeMirror editor.

In the HTML component, there is no longer a tabbed CodeMirror Editor. STUD-1516.
Use the correct response when using login.
Merge pull request #3253 from edx/sarina/fix-capa-calls

Explicitly declare `tags` in dog stats increment calls
Merge pull request #3244 from edx/christina/latex-bug-release

Fix source editor for the case of no CodeMirror editor.
Merge pull request #3256 from edx/diana/fix-grading-service-login

Return correct response when using _try_with_login
Revert "updated pdf viewer"

This reverts commit b0a7443570d929e705c295c1511f3188f4e41f69.
Revert refund instruction message
Merge pull request #3265 from edx/flowerhack/refund-message-patch

Revert refund instruction message
Refactor speed control.
Add fixes.
Update docstrings.
Removed unused helpers.
Fixed import of "dog_stats_api" in staff_grading_service.py.
LMS-2521