Implement first version of signing up / logging in with ParseUser

username = phoneNumber
password = phoneNumber
phoneNumber = phoneNumber
email not supplied.
Wire up our Person class to extend ParseUser

Person class enables us to have a wrapper that implements the getters and setters we want for the user profile fields.

Not a lot of error checking yet and no progress indicators - server calls can take quite a while.

On login screen, type your phone number then tap Get Started. If you do not yet have a user on the server, one will be created via the Sign Up process. If you do have a user up there, then you will be logged in using your phone number (username, password and phoneNumber are all set to your phone number).

Once you are successfully logged in and get to the MainActivity, you can use the following code to get the current user:

	Person user = (Person) ParseUser.getCurrentUser();
       if (user != null) {
            Toast.makeText(getActivity(), "got current user", Toast.LENGTH_SHORT).show();
       } else {
            Toast.makeText(getActivity(), "no current user", Toast.LENGTH_SHORT).show();
       }

Implement static method in CTRestClient - getPersonByPhoneNumber