Added support for editing users.

Currently insecure - next up: authorization
Non-signed in user is redirected when editing

This prevents a non-signed in user from editing a user's details. It
does not however stop a signed in user from editing anyone's details.
Only the right signed in user can edit users

Unauthorized users are redirected to the home page. Signing in now
implements friendly redirecting
Added index view to see whole list of users
Added concept of admin user who can delete users