Some jquery magic for the external sites forms

Hide the form fields if the account is not enabled using the slide
animation.

Disable the brightcove feed import fields if feed import is not
enabled.  Fixed the form to handle the feed_type input being disabled.
Make the team feed pages admin-only (#1435)
Fix tag handling for brightcove feeds (#1431)

Allow spaces in tags, use commas to separate them in the form.  Quote
tag text for feed URLs.  Add the "/tags" path component to feed URLs.

Added some helper text when entering tags.
Set initial values for brightcove feeds if one is saved (#1434)
Add migration to allow NULL added_by (#1430)