Clarify relation recursion and cardinality

Currently the partof facet seems to be recursive by default as suggested by these [IDS](https://github.com/buildingSMART/IDS/blob/master/Documentation/testcases/partof/pass-an_aggregate_entity_may_pass_any_ancestral_whole_passes.ids) and [IFC](https://github.com/buildingSMART/IDS/blob/master/Documentation/testcases/partof/pass-an_aggregate_entity_may_pass_any_ancestral_whole_passes.ifc) files.

This isn't very clear for example in the case when there's an assembly that contains another assembly that contains a slab and the slab is required to be part of one assembly. Would that cardinality fail in this case, since it is indirectly contained in two?

Should there be a flag in the partof requirement explicitly saying whether it should be applied recursively? Or should the relation be traversed until a parent is found that fits the requirement and stop there?

Also now it is not possible to require a direct relationship. A flag would help also in that case.