Set `en.titles.application` to App Name

* Gives developers that are unfamiliar with Caleb's `title` gem a nice hook to
  get started with

* **NOTE** currently failing because `i18n-tasks` sees `en.titles.application` as unused. Is there a way to:
  * ignore particular keys (and their children) in `i18n-tasks`
  * have `i18n-tasks` include gems (in this case, `title`) in their static analysis path