to be REST we will need a way to navigate to the individual `/applications/{appId}` URL's, via links.

that's not essential right now, but so that we *are able* to do this in future if needed, i suggest we introduce a new type, such as

    class UageStatistics {
        List<UsageStatistic> statistics;  // recalling that we rename Statistic to UsageStatistic
        Map<String,String> links;  // this can be empty, but having it gives us a place to make it REST, 
                                    // e.g. /apps endpoint can link to /apps/{id}
    }