Added event for removed comments with some refactoring

app/EventBuilder/BaseEventBuilder.php

@@ -0,0 +1,23 @@
+<?php
+
+namespace Kanboard\EventBuilder;
+
+use Kanboard\Core\Base;
+use Kanboard\Event\GenericEvent;
+
+/**
+ * Class BaseEventBuilder
+ *
+ * @package Kanboard\EventBuilder
+ * @author  Frederic Guillot
+ */
+abstract class BaseEventBuilder extends Base
+{
+    /**
+     * Build event data
+     *
+     * @access public
+     * @return GenericEvent|null
+     */
+    abstract public function build();
+}