Filters: Add filter for bloginfo to remove http(s) from urls.

Make css/js urls protocol agnostic.

Fixes gh-312
It looks like we can replace this with:

```php
add_filter( 'theme_root_uri', function( $url ) {
	return preg_replace( '/^https?:/', '', $url );
}, 10, 1 );
```

Which would make the existing calls to `get_*_directory_uri()` use protocol-relative URLs. This would prevent us from regressing with new code.