Update Login class to return login screen with reset _POST

Login class checks if AJAX_PAGE is set to true and then does not print
the login html to the screen directly, but returns it in the _POST array
login_html, _POST action is set to login
It also resets _POST & _GET arrays before hand to avoid any misuese.
All _SESSION array access needs to be checked in any following class as
the _SESSION is unset in this moment

html element should be overwritten with this JS:
document.getElementsByTagName('html')[0].innerHTML  =
data.content.login_html;

www/lib/CoreLibs/Admin/Backend.php

@@ -193,7 +193,7 @@ class Backend extends \CoreLibs\DB\IO
 		}
 
 		// get the session pages array
-		$PAGES = $_SESSION['PAGES'];
+		$PAGES = isset($_SESSION['PAGES']) ? $_SESSION['PAGES'] : null;
 		if (!isset($PAGES) || !is_array($PAGES)) {
 			$PAGES = array();
 		}