Ability to toggle admin status live

[notexactlyawe]

Currently I believe there is an admins.txt file that contains the email addresses of the admins in the application. This means that you can change the admins before starting the app, but not whilst it's running, which is really annoying when you want to add new volunteers.

Might be something to put in the users panel?

Requirements:

• Should only be visible to admins
• Should allow admins to be toggled on and off
• Should not allow you to toggle yourself off
• Should have a confirmation dialogue
• When toggled off, a user should not still have admin privileges