Add delete forms for media/feeds

Delete form for media was missing, this adds it back, improves it and adds tests.

While I was at it, I went ahead and added feed deletion as I'm sure this feature will come in handy.
Good question.  I think it is okay.  Any user can create a new feed when adding media or at any other time.  There is no flag in the database to denote a generated "user" feed, and users can edit the titles of their feeds.