Add basic support for exposing Customer.shoppers

now there is a Shoppers field when viewing a Customer, unless
configured otherwise

also tweaked some logic for navigating Customer/Person relationships,
to handle implications of Shoppers being (maybe) present

tailbone/views/master.py

@@ -4878,7 +4878,7 @@ class MasterView(View):
                 elif simple.get('type') is bool:
                     value = config.getbool(simple['section'],
                                            simple['option'],
-                                           default=False)
+                                           default=simple.get('default', False))
                 else:
                     value = config.get(simple['section'],
                                        simple['option'])