Update the sandbox alerting cookbook to point at a current example.
Merge pull request #661 from mozilla-services/cookbook_update

Update the sandbox alerting cookbook to point at a current example.
- fixed a bug where the name was not lowercased before looking it up in
  translations
- ignore empty capture values when looking up translations, as opposed
  to throwing errors, allows the other translations to execute.
  Non-empty untranslateable values still error