Feature work schedule (#1419)

* ifcopenshell.api modules Persons and Organisations account for IFC4 SCHEMA CHANGE

* New Feature to manpiulate Work Plans

src/ifcopenshell-python/ifcopenshell/api/sequence/assign_workplan.py

@@ -0,0 +1,31 @@
+import ifcopenshell
+import ifcopenshell.api
+
+class Usecase:
+    def __init__(self, file, **settings):
+        self.file = file
+        self.settings = {
+            "work_schedule": None,
+            "work_plan":None,
+        }
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        ###Project declaration should be removed if the workschedule is assigned to a project.####
+        if self.settings["work_schedule"].HasContext:
+            rel_declares = self.settings["work_schedule"].HasContext[0]
+            related_definitions = list(rel_declares.RelatedDefinitions)
+            related_definitions.remove(self.settings["work_schedule"])
+            rel_declares.RelatedDefinitions = related_definitions
+        if self.settings["work_plan"].IsDecomposedBy:
+            rel_aggregates = self.settings["work_plan"].IsDecomposedBy[0]
+            related_objects = list(rel_aggregates.RelatedObjects or [])
+            related_objects.append(self.settings["work_schedule"])
+            rel_aggregates.RelatedObjects = related_objects
+        else:             
+            rel_aggregates = ifcopenshell.api.run("aggregate.assign_object", self.file, **{
+                "product": self.settings["work_schedule"],
+                "relating_object": self.settings["work_plan"]
+            })
+        return rel_aggregates