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 think the "if you didn't make the request, you don't need to take any action" part of the message is not as clear as it previously was. Perhaps something stronger than "...and do not activate the account" and/or changing the order of the phrases.
Something like" If you did not request creating this account, you do not need to take any action; you will no longer receive emails from edX."