Restricted access of the Resque Dashboard to admins only

Think I fixed the issue. Added a controller. Only other strange thing would be in routes.rb. If the admin permission fails, it falls through and calls the default controller I created, which just checks the permission again with CanCan and displays the flash message like we discussed.

Hopefully this resolves enhancement #968 in Redmine. There's a little more information in the write up there.