break out urbanopt_load class to its own file

geojson_modelica_translator/geojson/urbanopt_load.py

@@ -0,0 +1,20 @@
+class GeoJsonValidationError(Exception):
+    pass
+
+
+class UrbanOptLoad:
+    """An UrbanOptLoad is a container for holding Building-related data in a dictionary. This object
+    does not do much work on the GeoJSON definition of the data at the moment, rather it creates
+    an isolation layer between the GeoJSON data and the GMT.
+    """
+
+    def __init__(self, feature):
+        self.feature = feature
+        self.id = feature.get("properties", {}).get("id", None)
+
+        # do some validation
+        if self.id is None:
+            raise GeoJsonValidationError("GeoJSON feature requires an ID property but value was null")
+
+    def __str__(self):
+        return f"ID: {self.id}"