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

src/ifcopenshell-python/ifcopenshell/api/constraint/add_objective.py

@@ -0,0 +1,15 @@
+import ifcopenshell
+
+class Usecase:
+    def __init__(self, file, settings={}):
+        self.file = file
+        self.settings = {}
+        for key, value in settings.items():
+            self.settings[key] = value
+
+    def execute(self):
+        return self.file.create_entity("IfcObjective", **{
+            "Name": "Unnamed",
+            "ConstraintGrade": "NOTDEFINED",
+            "ObjectiveQualifier": "NOTDEFINED"
+        })