- Internationalize upload errors.
- Move upload tests into their own files.
- Refactor upload dialog acceptance tests.

Authors can upload an image (or choose an existing one) from the
settings page, using the in-context uploader from PDF
textbooks. Includes tests for backwards compatibility with XML courses
-- they used a magic filename (images/course_image.jpg) which is
mapped to a location in the Mongo contentstore.

Still needs some UX work, though the backend plumbing is there.

Previously the file upload dialog was PDF- and textbook-specific. The
changes are adding parameters to the FileUpload model for the file
type, and adding an onSuccess callback to the UploadDialog view. Also
moved upload-specific SASS into its own file.

This was confusing translators as didn't make sense in English

switch the notification to be a prompt and allow for the user to go to the edit unit page which contains the module in error. Otherwise, present the raw exception message and allow user to go to the course outline page.

Also fixes a bug where message was not sent to user when entering 'denied'
state unless the user was previously in 'granted'.

Send notification to admin when a user enters 'pending' state.

Pylint cleanup.

This is to be used with VideoAlpha's functionality allowing a choice
of multiple HTML5 video sources.

alter the HTML editor so that it can do the /static/ <--> /c4x/ substitutions when toggling back and forth between the visual and advanced editors

have the Files and Upload pages surface a 'portable_url' which uses the /static/ shorthand which is more portable across course runs

Updates comment
Make Model descriptor class property.
Fix tests

Initialize on every page that has a context_course set

Hitting "Add User" with no email address, or trying to add a user to the course
team multiple times

Our designers find it helpful to be able to stub out simple views that aren't ready
to be seen for production yet, and check them into version control so that other
people can see them and provide feedback. This commit introduces a few new files
and directories for this purpose, as well as a sample view that will only be seen
in dev mode, and never in production.