Add incident column for when an incident occurred at (#2212)

Add incident column for when an incident occurred at. Closes #2208
[ci skip] [skip ci]

app/Bus/Exceptions/Incident/InvalidIncidentTimestampException.php

@@ -0,0 +1,25 @@
+<?php
+
+/*
+ * This file is part of Cachet.
+ *
+ * (c) Alt Three Services Limited
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace CachetHQ\Cachet\Bus\Exceptions\Incident;
+
+use CachetHQ\Cachet\Bus\Exceptions\ExceptionInterface;
+use Exception;
+
+/**
+ * This is the invalid incident timestamp exception.
+ *
+ * @author James Brooks <james@alt-three.com>
+ */
+class InvalidIncidentTimestampException extends Exception implements ExceptionInterface
+{
+    //
+}