Admins need to be able to book things

[amcewen]

Once you're an admin you can't then act as a user, we should make admins a superset of users.

[johnmckerrell]

This is managed by the users_roles table, if you are both a member and an admin you are able to administrate and also book things. We need some UI to allow us to add admin privilege to existing users as this doesn't appear to be a feature.