Plugin manager, misc fixes

* Fixed an error when trying to create nonexisting resource type
* Updated the init-command to create plugins and scipts directories
* Added a basic installer function

src/Resource/ResourceManager.php

@@ -18,6 +18,9 @@ class ResourceManager
 
     public function createResource(string $type, array $options)
     {
+        if (!array_key_exists($type, $this->resourceTypes)) {
+            return null;
+        }
         $resource = new $this->resourceTypes[$type]($options);
         return $resource;
     }