[CORE] Move public resources to a /public directory

Advantages:
* Increases security by preventing direct access to file/
* We are careful and have a defined('GNUSOCIAL') || die() to prevent
  direct access to GS files, but we may miss one or a vendor/extlib may
  not be as careful
* Improves directory structure - It's more natural to physically
  separate what is public from what are GNU social resources

plugins/TabFocus/tabfocus.js

@@ -1,7 +0,0 @@
-jQuery(function($){
-  $('#notice_data-text').bind('keydown',function(e){
-    if (e.which==9) {
-      setTimeout(function(){  $('#notice_action-submit').focus();  },15);
-    }
-  });
-});