added support for dynamic content controllers

Also implemented a placeholder generator to showcase it

content-controllers/text/text.controller.php

@@ -2,6 +2,8 @@
 
 class TextController implements ContentController
 {
+    public const ctype = 'static';
+    
     //returns all extensions registered by this type of content
     public function getRegisteredExtensions(){return array('txt','text','csv');}