Perform deep clone when cloning a part.

Fixes issue #25.

src/Entity/Base/AbstractNamedDBElement.php

@@ -89,7 +89,15 @@ abstract class AbstractNamedDBElement extends AbstractDBElement implements Named
     public function setName(string $new_name): self
     {
         $this->name = $new_name;
-
         return $this;
     }
+
+    public function __clone()
+    {
+        if ($this->id) {
+            //We create a new object, so give it a new creation date
+           $this->addedDate = null;
+        }
+        parent::__clone(); // TODO: Change the autogenerated stub
+    }
 }