Use `app.listen`, add "started" event, simplify explorer integration

Depends on strongloop/loopback#124
Related to #34, especially see [this comment](https://github.com/strongloop/loopback-workspace/issues/34#issuecomment-31818533).

This patch is not the ultimate solution, consider it as the first of many steps required to get where we want be with the app.js template.

/to @ritch please review
/cc @sam-github