Responses to Adam's comments; reset common.py, i18n compliance, deleted extraneous email.html file, fixed an HttpResponse, deleted unnecessary commented-out code, some small style tweaks

set max enrollment for downloads to 200

Add EmptyDataRawDescriptor.

Valera/carry over of add option transcripts remove onhover 2

Course Modes Expiration

There were previous merge conflicts in the file.

When auto-show/auto-hide is disabled, the captions will be shown when
the user will move the mouse over the "CC" button. They will then
auto-hide after a while if the user doesn't continue to move the
mouse over the "CC" button, or over the captions themselves, or use
the keyboard to select a specific caption. If the mouse pointer is not
over the captions or the "CC" button, they will hide after a while.

This is the key in the fix for bug BLD-355: Transcript hovers over
over videoplayer itself for PKU videos.

Front-end functionality was not removed. When flag is set to "True", old
behaviour of autohiding of controls and captions will be enabled.

Delete on publish to prevent orphans

Use wrapped tar extraction

Signed-off-by: Julian Arni <julian@edx.org>

Bug fix video player controls a11y