Add basic method for admins adding new admins.

This also includes an incidental change to the way user ids
are retrieved from the DOM to be sent in the ajax request.
Fix gitignore for new test db script.
Improve adding more admins.

Multiple admins can now be added at a time and the view shows buttons for only users
who are not yet admins. Also add an api route for resigning from the administration of a
group.