Handling o multiple slicestacks in a components-hierarchy is not clear

[martinweismann]

The slicespec allows to define slicestacks on any object, as per https://github.com/3MFConsortium/spec_slice/blob/master/3MF%20Slice%20Extension.md#object

Thus, you can refer to a slicestack from a componetsobject A and from a different object B, which is referenced from this componentsobject.

Problem: it is not clearly specified, which slicestack-representation takes precedence, how/if they are merged, or in general, how this situation is handled.

Example:

problematic.txt

[jordig100]

The way that HP has implemented it is by acknowledging the hierarchy. If a Components object has defined a slicestack it would take it as the representation of the components, and discarding the individual representation of each component.

I propose to consolidate this behaviour by documenting it.

Let's propose a test case to cover it.

[jordig100]

Added the following paragraph to the spec under Object:

The slicestack MIGHT be defined into components object providing a slicestack for the combined components or into an individual mesh object. When the slicestack is defined in both types of objects, the slicestack that prevails MUST be the one at the components level.

[JimZuber]

New test case added the will demonstrate if the printer select the right precedence between a slicestack defined at the object or component level.