Add thumbnail images to Appliances grid

guess we'll see how folks like this

tailbone/views/master.py

@@ -106,6 +106,7 @@ class MasterView(View):
     executing = False
     has_pk_fields = False
     has_image = False
+    has_thumbnail = False
 
     row_attrs = {}
     cell_attrs = {}
@@ -871,6 +872,22 @@ class MasterView(View):
     def get_image_bytes(self, obj):
         raise NotImplementedError
 
+    def thumbnail(self):
+        """
+        View which renders the object's thumbnail image as a response.
+        """
+        obj = self.get_instance()
+        image_bytes = self.get_thumbnail_bytes(obj)
+        if not image_bytes:
+            raise self.notfound()
+        # TODO: how to properly detect image type?
+        self.request.response.content_type = str('image/jpeg')
+        self.request.response.body = image_bytes
+        return self.request.response
+
+    def get_thumbnail_bytes(self, obj):
+        raise NotImplementedError
+
     def clone(self):
         """
         View for cloning an object's data into a new object.
@@ -3002,6 +3019,12 @@ class MasterView(View):
             config.add_view(cls, attr='image', route_name='{}.image'.format(route_prefix),
                             permission='{}.view'.format(permission_prefix))
 
+        # thumbnail
+        if cls.has_thumbnail:
+            config.add_route('{}.thumbnail'.format(route_prefix), '{}/{{{}}}/thumbnail'.format(url_prefix, model_key))
+            config.add_view(cls, attr='thumbnail', route_name='{}.thumbnail'.format(route_prefix),
+                            permission='{}.view'.format(permission_prefix))
+
         # clone
         if cls.cloneable:
             config.add_tailbone_permission(permission_prefix, '{}.clone'.format(permission_prefix),