lib: Add SecurityException

All assertPermission() calls must throw this exception.

library/Icinga/Security/SecurityException.php

@@ -0,0 +1,12 @@
+<?php
+
+namespace Icinga\Security;
+
+use Icinga\Exception\IcingaException;
+
+/**
+ * Exception thrown when a caller does not have the permissions required to access a resource
+ */
+class SecurityException extends IcingaException
+{
+}