Authentication

Adds Dependancies: 
* Devise: Easy user creation/authentication
* binding_of_caller: In browser debugging (works with better_errors)

Adds User model

Adds associations:
* User -> Companies
* User -> PaymentMethods
* User -> Companies -> Payments

Moves navigation into a partial.

All resources are now pulled from the current_user, ensuring user A can not view user B's resources.