WIP port object material assignment with 3 new features. See message. See #1222.

* Full support for editing IfcMaterialList added
 * The reusability of material set relationships are now roundtripped
 * UI is sensitive to IFC schema version and adapts intelligently

src/ifcblenderexport/blenderbim/bim/module/material/add_layer.py

@@ -0,0 +1,19 @@
+import ifcopenshell
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"layer_set": None, "material": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        layers = list(self.settings["layer_set"].MaterialLayers)
+        layer = self.file.create_entity("IfcMaterialLayer", **{
+            "Material": self.settings["material"],
+            "LayerThickness": 0.
+        })
+        layers.append(layer)
+        self.settings["layer_set"].MaterialLayers = layers
+        return layer