[feature/avatars] Add subsilver2 support

This implementation might not be perfect though.

PHPBB3-10018

phpBB/styles/subsilver2/template/avatars.js

@@ -0,0 +1,15 @@
+(function($) {  // Avoid conflicts with other libraries
+
+"use strict";
+
+function avatar_simplify() {
+    $('.[class^="av_option_"]').hide();
+
+    var selected = $('#avatar_driver').val();
+    $('.av_option_' + selected).show();
+}
+
+avatar_simplify();
+$('#avatar_driver').bind('change', avatar_simplify);
+
+})(jQuery); // Avoid conflicts with other libraries