Enable monitoring (rebased version)

You might not see the logs, but that's expected (see #796).

also, to try it, you have to:
- use play `2.3.8-2de45b3774b6757f4aae980f8b5b152c1d2b73a5` in `play.sbt`
- publish locally sbt-nr and sbt-ad (the specific `wip/h3nk3-play-specific-plugin` branch) - **not needed any longer as the plugins have been published publicly now**
Not for now, but I think most of this file can be replaced with sbt's IO stuff.  Yes, I know I'm the original offender in this case. :-)