Switch ResourcesAnalyzer API to use a factory method

At present, client code of ResourcesAnalyzer (in <SearchAndSort>) simply creates objects using new ResourcesAnalyzer. But we want to be able to make either a stripes-connect or GraphQL-based analyzer depending on the props that are available. To do that we need to use a makeResourcesAnalyzer function that returns a new instance of one or other of the underlying analyzer classes.