- macroId(element) returning a globally unique consecutive integer id
- master(element)  returning the master process for the given entity
- weight(intersection) returning (an upper bound) for the communication cost for this intersection
With these three methods a dune sided call to a graph partitioner (e.g. Zolan) becomes possible.
The three methods can also be moved to the Entitiy/Intersection class but this approach a better capsulation of
the new features. The weight method does not take anything like filtering, possible communication on
not leaf level into account, or varying sizes for the communicated data into account...