Make helpers for checking user permissions

[Noah-Huppert]

Make a suite of helper methods for checking to see if the client making the api request has the correct permissions.

Models::ApiAccessToken.from_request(request): Creates an ApiAccessToken from a Http request. If an access_token is not present one will be created with a null user_id and a null expires_on

Models::User.from_access_token(access_token): Creates a User from an ApiAccessToken. If the user_id feild in the ApiAccessToken is null then a user will be created as per #23

[Noah-Huppert]

Done!