Remove modernizr.js and use html5shiv.js directly.
Use a CSS sprite for the homepage images.

-2 http requests, -1KB.
licenses.html: Add missing page title.
_includes/license-overview.html: Fix validation errors.

Include the `id` only if `variation.tab-slug` is set.
Merge pull request #155 from XhmikosR/home-sprite

Home sprite
Merge pull request #158 from XhmikosR/licenses-title

licenses.html: Add missing page title.
Merge pull request #157 from XhmikosR/html5shiv

Remove modernizr.js and use html5shiv.js directly.