Use 'type="email"' for email inputs in registration and settings templates.

This provides a better experience on mobile devices and other browsers that
support the 'email' type.

Props standardspace.
See #5914.

git-svn-id: https://buddypress.svn.wordpress.org/trunk@9225 cdf35c40-ae34-48e0-9cc9-0c9da1808c22