Move OTYPE constants to own enum class

src/Model/Notify/ObjectType.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace Friendica\Model\Notify;
+
+/**
+ * Enum for different otypes of the Notify
+ */
+class ObjectType
+{
+	const PERSON = 'person';
+	const MAIL   = 'mail';
+	const ITEM   = 'item';
+	const INTRO  = 'intro';
+}