jquery: Add the js class, remove the no-js one

This used to be done by Modernizr until its removal in
08f27c1. Some sites apply different styling for
JS-disabled environments; one such example is the jQuery UI Download Builder
which expands all Themeroller knobs sections in the no-JS mode.

themes/jquery/js/main.js

@@ -2,6 +2,9 @@
  * All sites
  */
 $(function() {
+	// Some CSS depends on the `js` class.
+	$( "html" ).addClass( "js" ).removeClass( "no-js" );
+
 	// copyable auto-select-all
 	$( ".copyable" ).on( "click", function() {
 		if ( typeof this.select === "function" ) {