Fxa email popup 1052876

https://bugzilla.mozilla.org/show_bug.cgi?id=1052876
https://bugzilla.mozilla.org/show_bug.cgi?id=1065725

When a "migratable" user starts the login they will be shown the FxA migration dialog describing the migration and redirecting them to login/register based on their email address.

![fxa-migration mov](https://cloud.githubusercontent.com/assets/211578/4391855/f04a9cf0-4408-11e4-9aa9-b9dde6fbb5ac.gif)

I just opened it in the popup window but am running into problems now. I'm going to try making it use the regular rendering but I'm unsure of how the CSS will co-exist.