Redirect requests for /apple-touch* to the assets

Seems like iOS (and Android) request /apple-touch-icon.png and its variants, resulting in a pile of 404s on the main site.

This is explicitly against [Apple's own documentation](http://developer.apple.com/library/ios/#documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html), which says iOS respects the `link` elements we've added, but as the logs don't lie we should serve a 301 to the right place here. The 301s will get cached and stop bothering us.