Start the complete_sign_up screen.

* Fetch the code, uid, and service from the URL search string.
* Handle errors
* In the create_account screen, only attempt to create an account if both email and password are available.
* rename tests/functional/signIn.js => sign_in.js and signUp.js => sign_up.js for consistency.
Merge pull request #195 from mozilla/issue-194-email-verification-screens

email confirmation flow.