Admins cannot deploy channels for which they are not editors

[rtibbles]

Observed behavior

Clicking on 'deploy' for a ricecooker staged channel results in a 404 when trying to access /api/activate_channel/ if the user is an admin but not an editor for the channel.

Expected behavior

Admins should be able to deploy any channels.

This is a result of the edit_queryset_filter method not taking into account user admin status.