fix bug 1059055 - Move PromoteJS out of MDN codebase
Fix bug 866533, 1054559: Update registration page

Update the registration page copy (bug 866533). In updating the copy, we
ensure that the copy is visible even when a user signs in with GitHub
(bug 1054559).
bug 866533 - tests for sign-in and sign-up pages
bug 866533 - remove unused attribute values from signup form
Merge pull request #2705 from darkwing/remove-promote-js

fix bug 1059055 - Move PromoteJS out of MDN codebase
Merge pull request #2698 from groovecoder/registration-copy-866533

Fix bug 866533, 1054559: Update registration page