Level set (N-1)/N

LevelSet shaped bodies can now interact (without touching InteractionLoop as discussed at some point in the past). Example has been extended in this aspect and a check test is introduced.

New examples might come in the future but this concludes anyway !779 (merged) and !797 (merged) in the sense we have now a working stage for LevelSet shape description (outside direct visualization in YADE, which does exist on any computer as of now..)