Fix Bug 1087579 - Update email preference center copy & layout to accommodate Newsletters vs. Interests for One-off emails

See [this screeshot](https://bugzilla.mozilla.org/attachment.cgi?id=8527903) how it works. Should be live on December 8.
The travis failure is due to flake8: we still need `# noqa` because these are imported without being used in the same file. :(