Switch to `grunt-usemin`.

Now every asset is properly renamed so that there should be no cache issues anymore.
Add `grunt-uncss`.

~-25% from the CSS size.
Enable htmlmin's `removeAttributeQuotes` option.
README.md: Switch to the SVG badge.
Update highlight.js to v8.1.
Update dependencies.
Update Apache config to v2.7.1.
Merge branch 'XhmikosR-master'