First attempt at ripping out agnostic code into ifcopenshell.api namespace. See #1399.

src/ifcopenshell-python/ifcopenshell/api/owner/add_role.py

@@ -0,0 +1,11 @@
+class Usecase:
+    def __init__(self, file, settings=None):
+        self.file = file
+        self.settings = {"assigned_object": None}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        roles = list(self.settings["assigned_object"].Roles) if self.settings["assigned_object"].Roles else []
+        roles.append(self.file.createIfcActorRole("ARCHITECT"))
+        self.settings["assigned_object"].Roles = roles