Added duplicate video failed status for VAL.

As some i18n features need ```ugettext``` or its shorcut ```_``` to be called on a non-string-literal, so the pylint check of ```translation-of-non-string``` should be explicitly disabled in such situations.

Imported VAL videos get the value "imported" for their status. We
considered not including imported videos on the upload page but have
instead decided to include them, so it is necessary to have a display
string for the imported status value.

MA-77 Automatically adds the course id to the videos in VAL
when a course is rerun.

Some status strings were accidentally tuples thanks to stray commas, and
ugettext raised an exception as a result.

JIRA: MA-323

This provides a better UX for video uploaders, because recent uploads
are readily visible at the beginning of the table.

This fixes two bugs:
1. All statuses were listed as "Unknown"
2. Non-ASCII characters in a header column translation resulted in a 500

This fixes two bugs:
1. All statuses were listed as "Unknown"
2. Non-ASCII characters in a header column translation resulted in a 500

Fix i18n for video status strings (broken in commit 4b53f4df) and remove
unnecessary complexity from a test case. This also removes the status
whitelist in the video upload configuration. Because status is included
in the CSV report, it is not necessary to filter the included videos by
status.

The button downloads the CSV data containing all video URLs.

The endpoint returns an Excel-dialect CSV file for download.

Co-authored-by: Chris <crodriguez@edx.org>
Co-authored-by: Mark Hoeber <hoeber@edx.org>

This feature allows upload of video assets to S3. This requires that the
VIDEO_UPLOAD_PIPELINE setting be properly configured and that each
course be configured with a token issued by the media team for their
processing purposes (e.g. linking the video with a YouTube channel).

Co-authored-by: Greg Price <gprice@edx.org>