.htaccess: Update CSP related configs
Fix positioning of `aside` icons on small screens

Close h5bp/html5boilerplate.com#119.
Base64 encode the background images.

-2 HTTP requests and CSS size is +1.5KB of what it was before grunt-uncss (8.47KB minified without gzip).
Remove old IE hacks.
Update normalize.css to v3.0.1.