Don’t allow use of .get() on service model

Making people use a property is a sure way to make sure they’re spelling
the name of the property correctly, and allows us to easily swap out
properties that call through to the underlying JSON, and properties
which are implemented as methods.

The API should always return something in the JSON for a property, even
if it’s just `None`.

app/models/service.py

@@ -53,10 +53,9 @@ class Service():
         )
 
     def get(self, attr, default=None):
-        try:
-            return self._dict[attr]
-        except KeyError:
-            return default
+        raise NotImplementedError(
+            'Use current_service.{} instead of current_service.get(\'{}\')'.format(attr, attr)
+        )
 
     @property
     def trial_mode(self):