Make sure "configure" pages use AppHandler to save/delete settings

so that beaker config cache is invalidated, if in use

tailbone/views/vendors/core.py

@@ -202,8 +202,7 @@ class VendorView(MasterView):
 
     def configure_remove_settings(self, **kwargs):
         super(VendorView, self).configure_remove_settings(**kwargs)
-
-        model = self.model
+        app = self.get_rattail_app()
         names = []
 
         supported_vendor_settings = self.configure_get_supported_vendor_settings()
@@ -211,11 +210,11 @@ class VendorView(MasterView):
             names.append('rattail.vendor.{}'.format(setting['key']))
 
         if names:
-            # nb. we do not use self.Session b/c that may not point to
-            # the Rattail DB for the subclass
-            Session().query(model.Setting)\
-                     .filter(model.Setting.name.in_(names))\
-                     .delete(synchronize_session=False)
+            # nb. using thread-local session here; we do not use
+            # self.Session b/c it may not point to Rattail
+            session = Session()
+            for name in names:
+                app.delete_setting(session, name)
 
     def configure_get_supported_vendor_settings(self):
         app = self.get_rattail_app()