add copy to ZonedPluginRegistry

src/pluginbase.py

@@ -1,4 +1,14 @@
+from abc import abstractmethod
+
 
 class PluginBase():
     def __init__(self):
         pass
+
+    @abstractmethod
+    def copy(self):
+        """
+        Subclasses that use state must implement this method and return a new instance of themselves.
+        :return:
+        """
+        return self