Jwang add resource measurements

This method is for serving the REST API call to fetch resource usage of a particular query given its query id, but `ResourceUsage` is a map from subquery ids to their stats. This blanket search is simply for mapping a query id to all its subquery ids, I believe it's the correct place. 

How do you feel about letting the user provide a subquery id, instead of a query id, through the REST API? In this case the blanket search can be avoided. Plus, we currently only support profiling a qsubquery with subquery id = 0.