Standard streams

As I think we discussed IMO "transport" and "sport" are too arbitrary. Better have "transport" alongside "walking", "running", "cycling" etc.

+ then of course we should have the substreams (e.g. for transport: "car", "train"...) as Perki convinced me it was more correct. (But then it means we should fix how graphs aggregate in order to make things like a graph of total calories possible.)