N°3663 Group exception classes in /application/exceptions

Original files kept for compatibility issues :
- core/coreexception.class.inc.php

There are remaining exceptions in /core/oql, but those files are generated

application/exceptions/PageNotFoundException.php

@@ -0,0 +1,13 @@
+<?php
+/**
+ * @copyright   Copyright (C) 2010-2021 Combodo SARL
+ * @license     http://opensource.org/licenses/AGPL-3.0
+ */
+
+namespace Combodo\iTop\Application\TwigBase\Controller;
+
+use Exception;
+
+class PageNotFoundException extends Exception
+{
+}