remove regular Extension, have SimpleExtension take its place, optimise the event system based on SimpleExtension methods

contrib/qr_code/main.php

@@ -7,7 +7,7 @@
  *              Further modified by Shish to remove the 7MB local QR generator
  *              and replace it with a link to google chart APIs
  */
-class QRImage extends SimpleExtension {
+class QRImage extends Extension {
 	public function onDisplayingImage(DisplayingImageEvent $event) {
 		$this->theme->links_block(make_http(make_link('image/'.$event->image->id.'.jpg')));
 	}