Arch: Handle multilayer walls - when joining walls together the layers should be unioned by material

Issue imported from https://tracker.freecad.org/view.php?id=2880

* **Reporter:** yorik
* **Date submitted:** 1/29/2017
* **FreeCAD version:**
* **Category:** Feature
* **Status:** assigned
* **Tags:**

# Original report text

When creating a "father" wall (when inserting windows), multilayer walls are disregarded. This should be handled properly.

# Additional information

Discussion topic: https://forum.freecadweb.org/viewtopic.php?f=23&t=20316

# Other bug information

* **Priority:** normal
* **Severity:** minor
* **Category:** Feature
* **OS: Debian Testing 64bit**
* **Platform:** PC
* **Updated:** 2/6/2021

# Discussion from Mantis ticket

### Comment by Kunda1 2017-11-04 12:34
yorik does the issue also cover "Allow to convert multilayer wall to multiple walls and vice-versa" mentioned in http://yorik.uncreated.net/guestblog.php?2017=414 or should I open a separate ticket for that?