Move ITemplateEngine to src

- Fix method name format

src/Render/ITemplateEngine.php

@@ -0,0 +1,15 @@
+<?php
+/**
+ * @file src/Render/ITemplateEngine.php
+ */
+
+namespace Friendica\Render;
+
+/**
+ * Interface for template engines
+ */
+interface ITemplateEngine
+{
+	public function replaceMacros($s, $v);
+	public function getTemplateFile($file, $root = '');
+}