Allow grace periods of > 24 hours.

Made the lambda statement more resistant to errors

Made the statement better

pylint fix

Accidently left off parameter

Removed logout

WIP: Peter fogg/course image upload

update the PDF textbook url paths as well as update wiki_slug when impor...

Move course modes to common and enable in Studio admin

Make it so that students who are not enrolled cannot see the forum

Also change the file uploader to accept multiple file types.

- 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.

Remove js log_event (keep compatibility)

keep log_event for compatibility

Add docs for changes in #726

Fix failing grade label being editable but not saved.

Incorporate Anant's suggestions

Use calc's evaluator for staff answers in `Numercial` type