Make the persistence method of hanging protocols configurable

- Implement ProtocolStore interface to allow persisting hanging protocols using different strategies
- Implement and set default strategy to persist hanging protocols in the MongoDB collection “HangingProtocols” in the application server

LesionTracker/client/components/viewer/viewer.js

@@ -12,7 +12,6 @@ Template.viewer.onCreated(() => {
     ViewerData = window.ViewerData || ViewerData;
 
     const instance = Template.instance();
-    instance.subscribe('hangingprotocols');
 
     ValidationErrors.remove({});