UI to manage bridge troll admins

[ultrasaurus]

creating a UI for this is much lower priority that other things, since we should have very few global admins (and we really need better docs, before making it easy to add admins!)

right now, we can create admins via making changes to the production database on the console (eek!)

heroku console --app bridgetroll
u = User.find(51)
=> #<User id: 51, email: "rachel...
u.admin = true
u.save!