fix the 1-to-1 relationship between user and api_key;
add vehicles_controller;
update model of user with class instance variables token and token_status as well as their accessors;
add 1-to-many relationship between user and vehicle;
update model of vehicle with class instance variables user_id as well as its accessors;
update model of user with class instance variables vehicles;
implement class instance variables token and token_status on users_controller;
add sample mock car info as the seeder for vehicle;