Set email input field to type=email for better UX

Setting `<input type="email" ...>` instead of `<input type="text" ...>` makes for an awesome user experience.

There are some additional niceties on Desktop (address book integration, validation, etc.), but the big win is on Mobile, where browsers can show users a virtual keyboard tailored to entering email addresses.

## Before & After Screenshots:

![FxOS 2.0 Virtual Keyboards](https://cloud.githubusercontent.com/assets/24193/4047965/fdba0442-2d3e-11e4-92a6-671389ec69f7.png)

![iOS 7 Virtual Keyboards](https://cloud.githubusercontent.com/assets/24193/4047971/08a9e4c6-2d3f-11e4-969f-1df5c6a93491.png)