Add decorator for DisableCancelEmail

Similar to the confirm email, we need this to respect the
'disable_builtin_emails' value.

Author: kjriga

app/decorators/models/solidus_tracking/spree/order/disable_cancel_email.rb

@@ -0,0 +1,13 @@
+module SolidusTracking
+  module Spree
+    module Order
+      module DisableCancelEmail
+        def send_cancel_email
+          super unless SolidusTracking.configuration.disable_builtin_emails
+        end
+      end
+    end
+  end
+end
+
+Spree::Order.prepend(SolidusTracking::Spree::Order::DisableCancelEmail)