Couple of API tweaks for work orders

made a change to sorting such that it assumes the primary model is
being sorted, if caller does not specify

tailbone/api/master.py

@@ -177,17 +177,14 @@ class APIMasterView(APIView):
         """
         return self.sortcol(order_by)
 
-    def sortcol(self, *args):
+    def sortcol(self, field_name, model_name=None):
         """
         Return a simple ``SortColumn`` object which denotes the field and
         optionally, the model, to be used when sorting.
         """
-        if len(args) == 1:
-            return SortColumn(args[0])
-        elif len(args) == 2:
-            return SortColumn(args[1], args[0])
-        else:
-            raise ValueError("must pass 1 arg (field_name) or 2 args (model_name, field_name)")
+        if not model_name:
+            model_name = self.model_class.__name__
+        return SortColumn(field_name, model_name)
 
     def join_for_sort_spec(self, query, sort_spec):
         """