update AuthFragment to implement Registration;
add Registration activity to manifest.xml;
update the behaviors of registration button on AuthFragment;
implement registration.xml on Registration;
add message field and its getter and setter to ApiKey model;
minor text fix in registration.xml;
update AuthFragment to remove CM_USER_EMAIL and CM_USER_NICKNAME from SharedPreferences while sign out;
add message field and its getter and setter to User model;
add logic and callback to Registration;
update input verification logic on Registration;