Improve notification classes and move interface to core

app/Core/Notification/NotificationInterface.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Kanboard\Core\Notification;
+
+/**
+ * Notification Interface
+ *
+ * @package  Kanboard\Core\Notification
+ * @author   Frederic Guillot
+ */
+interface NotificationInterface
+{
+    /**
+     * Send notification to a user
+     *
+     * @access public
+     * @param  array     $user
+     * @param  string    $event_name
+     * @param  array     $event_data
+     */
+    public function notifyUser(array $user, $event_name, array $event_data);
+
+    /**
+     * Send notification to a project
+     *
+     * @access public
+     * @param  array     $project
+     * @param  string    $event_name
+     * @param  array     $event_data
+     */
+    public function notifyProject(array $project, $event_name, array $event_data);
+}