Extend "Relays by relay flags" graph to display flag combinations

When I select 'Running', 'Exit', and 'Fast' flags on this graph, I'm assuming it should return the number of "fast and currently running exit nodes" but instead of showing me a mix of all those things, it shows me the list of those flags separately. Hence it's unclear whether the list of exits that I'm seeing are all running or not.

Maybe we should have an / kind of filtering here?