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/unassign_material.py

@@ -0,0 +1,14 @@
+import ifcopenshell
+
+
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"product": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        for association in self.settings["product"].HasAssociations:
+            if association.is_a("IfcRelAssociatesMaterial"):
+                self.file.remove(association)