Move Authorization and Authentication plugin structures into core, instead of as plugins.

This move makes sense as you can addPlugin('Authentication') for example - these are abstract classes designed to be implemented, not used directly.

plugins/CasAuthentication/CasAuthenticationPlugin.php

@@ -34,7 +34,6 @@ if (!defined('STATUSNET') && !defined('LACONICA')) {
 // We bundle the phpCAS library...
 set_include_path(get_include_path() . PATH_SEPARATOR . dirname(__FILE__) . '/extlib/CAS');
 
-require_once INSTALLDIR.'/plugins/Authentication/AuthenticationPlugin.php';
 class CasAuthenticationPlugin extends AuthenticationPlugin
 {
     public $server;