Certificates: Add regeneration command

* Adds regenerate_user command, which lets you run certificates for one
  particular user in one particular class, regardless of whether they
  have a pre-existing certificate.
Merge pull request #1348 from edx/dhm/bug_publish

Delete on publish to prevent orphans
Move logic that decides whether to show shoppingcart to middleware

Middleware is a better place for this, rather than navigation.html
template
pep8 + pylint
Work in progress.
Updated code fomat in test Jasmine.
Added hard-coded flag to video.html that turns on/off autohiding of captions.

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

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.
Updated fixtures for Jasmine tests.
Added acceptance tests.
Updated acceptance tests.
Updated acceptance tests.
Fixing JS.

There were previous merge conflicts in the file.
Furthe addressing comments on PR.
Minor tweak.
Fixing minor typo.
Tidy up the code.
Fix acceptance tests.
Clean up the code.
Enabling showing of captions always when mouse is over CC.