[Feature Request] Better authentication

[eranimo]

I'm not really a fan of URL-based authentication, I'd rather have hashed and salted session-based authentication wherever possible. I also don't think that not having authentication should be possible. I propose emulating the Django user model method of authentication. Sequelize-admin would take in a user model (as specified), authenticate and store the session data it in a predefined session store. The admin panel would refuse access to all users not logged in or that do not have an optional model attribute representing the ability to access the admin panel.