provide API for periodic layers

Allow for hierarchical multilayer structure where one layer can consist of n repetitions of a substructure.

For concepts, see https://jugit.fz-juelich.de/mlz/intern/ba-intern/-/blob/master/internal_reports/2012_Polylayer.md and https://jugit.fz-juelich.de/mlz/intern/ba-intern/-/blob/master/randolf/Documents/200421%20RepeatingLayers%20API/RepeatingLayersAPI.pdf.

After change to Core API, this must also be supported in the GUI.

[Redmine2436]

At this occasion, support independent roughness cross-correlation for disjoint sets of interfaces [Redmine1677: would be appropriate for resonator example]