Create User model and login interface

[schneidmaster]

We'll want to have an admin interface for adding/managing Cleveland based companies (and maybe other website management things down the line).

We should add a User model -- it could either just use has_secure_password, or it can use something like Devise, up to whoever implements this. We'll need at least a controller/views for users to be able to log in (reset password/more advanced functionality could come later). We should also have an admin CRUD interface for users to be able to add/manage other users, and probably a role enum attribute on users (admin -- can manage the site and other users; manager -- can manage the site but not other users).