move want_replies into new plugin system

src/plugins/PositionPlugin.h

@@ -24,6 +24,12 @@ class PositionPlugin : public ProtobufPlugin<Position>
     @return true if you've guaranteed you've handled this message and no other handlers should be considered for it
     */
     virtual bool handleReceivedProtobuf(const MeshPacket &mp, const Position &p);
+
+    /** Messages can be received that have the want_response bit set.  If set, this callback will be invoked
+     * so that subclasses can (optionally) send a response back to the original sender.  Implementing this method
+     * is optional
+     */
+    virtual void sendResponse(NodeNum to);
 };
 
 extern PositionPlugin positionPlugin;