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

Packages/ohif-study-list/client/components/studylist/studylist.js

@@ -41,6 +41,4 @@ Template.studylist.onRendered(() => {
             switchToTab(contentId);
         }
     }
-
-    Meteor.subscribe('hangingprotocols');
 });