DON'T YET MERGE: Add start-status-command

We have to merge this PR once the respective [PR 236](https://github.com/typesafehub/reactive-runtime/pull/236) against RR has been merged. Then also create a 0.3.0 release, update sbt-reactive-runtime and create a 0.7.0 release for that.
Please remove the "start". As mentioned in the other PR, the status command can be used for at start time, and for periodic checking.