ID-36: Email selector UI

Here's the UI I put together for the edit-profile email address selector. There is one big item of functionality missing: **changing a current email address**. Without this, to change an email address you have to first add the new address, then delete the old one. Unless you think otherwise, I think we should implement this functionality.

You may want to hold off on approving & merging this PR until I commit the "change current email address" implementation.

Other code changes include rewriting the `style()` and `script()` helpers as middleware, some re-organization of {less} source, and routing changes to `emails.js` to make the front-end interface easier to use.