Vastly simplify Shingen

- hostgroups don't need to be explicitly declared, apparently :)
  Are implicitly picked up if they exist in a host definition.
- Collaps shingen script into one file. Originally shingen was
  supposed to be much more featurefull, similar to naggen2. However,
  that is no longer the case - it simply generates hosts definitions
  with appropriate hostgroups. So simplify architecture to fit
  purpose

Change-Id: Ied6ac68384c26443c067851517b65ef72f83cbde