Sylvia/docs/doc 1105

@lamagnifica @catong @mhoeber: This is a draft of the updates to the Register Your Account section to reflect the new login/registration page. The feature is currently in a/b testing, so we don't want to merge the branch yet, but feedback is still welcome.
I'd suggest putting "on edx.org or edge.edx.org" right up front, rather than hiding the URLs in the bullets.