Add the ViewSupplement concept

also fix cell-class for grid columns.  cannot use "raw" fieldname
because in some cases (e.g. 'number', 'rate') Bulma may interpret that
as actually meaning something, and affect the display

tailbone/views/vendors/core.py

@@ -165,7 +165,7 @@ class VendorView(MasterView):
             self.Session.delete(cost)
 
     def get_version_child_classes(self):
-        return [
+        return super(VendorView, self).get_version_child_classes() + [
             (model.VendorPhoneNumber, 'parent_uuid'),
             (model.VendorEmailAddress, 'parent_uuid'),
             (model.VendorContact, 'vendor_uuid'),