Relations order of relating and related attributes

I suggest to unify the order of relating and related attributes in objectified relations, particularly one-to-many relations. Currently we have for example:

* `IfcRelContainedInSpatialStructure` with many side first (`RelatedElements`), one side second (`RelatingStructure`)
* `IfcRelAggregates` with the one side first (`RelatingObject`), many side second (`RelatedObjects`)

This is a proposal to 'change' entities in the schema.

This would reduce variations in the schema which could cause confusion.

We would loose direction of the relation. If the relations are meant to be (and stay) uni-directional (or with a main direction), then this proposal would be obsolete. In that case I would still propose to check for consistency in names (subjects -relating- first, objects -related- second).

No impact on schema level, only on instance level. Instances are not forward-compatible. Automatic migration is possible.