Add user sessions
Although rails provides built-in user sessions, this allows us to add additional fields to the session model. For example, we can now track the user agent and IP address of all sessions associated with a user. Long term, this allows us to do neat things like session revocation (by both user and admin) and sudo mode.
See merge request !5
Add user creation
Adds simple creation of users that have a username, password, and an email. The password is managed by Rail's `has_secure_password`.
See merge request !2
