Support unicode email addresses

[pdehaan]

In #362 (comment) it looks like we don't support unicode/accented characters when creating an account (ie: josé@gmail.com will fail as an invalid email address).

In #362 (comment) @shane-tomlinson cites mozilla/persona#1294 Persona bug complaining about the lack of unicode support.

Cool story bro...
Well, now in http://googleblog.blogspot.com/2014/08/a-first-step-toward-more-global-email.html it looks like Google (they have a search engine thing) is making a push to support addresses with non-Latin and accented Latin characters.

Starting now, Gmail (and shortly, Calendar) will recognize addresses that contain accented or non-Latin characters. This means Gmail users can send emails to, and receive emails from, people who have these characters in their email addresses. Of course, this is just a first step and there’s still a ways to go. In the future, we want to make it possible for you to use them to create Gmail accounts.

Long story longer, we need to find a way to relax (or improve) the regex to allow people to use legit email addresses that fall outside the range of our a-z style regex validations.
Bonus points if we make it into an npm module or bower or something we can share between our projects.

[ckarlof]

Duplicate of #689.