Add User scaffold

rails g scaffold User steam_id:integer username:string avatar:string
signup_ip:string last_ip:string tf2r_user_id:integer is_admin:boolean
Fix User specs
Convert application.html to haml
Change auth path to /login
Change User username to nickname
Add user_id to Tf2rUser; update associations and validations
Add "navbar" to application layout
Fix up Tf2rUser specs for user_id
Add actual signing in
Add simple navbar
Record user ip on signin