Add demo tree if configuration hierarchy is empty (Follow-up from "Feature use configurations data model")

The following discussion from !38 (merged) should be addressed:

• @nils started a discussion: (+3 comments)

  If I would play "Wünsch dir was" I would like to have a kind of demo tree visible (as gray-ish image in the background) when I create a new configuration - so that the user has an impression of what this tree should look like.

  I know that this is a lot of work (so more a new issue), but the old demo configuration tree was really nice regarding to this. So loosing it completely I feel like we loose the chance to show how the tree should look like.