Remove System.out.printlns
Rename Reachability to StateSpaceExplorer
Restructure StateSpaceExploration, #52

* Split out the parts of the exploration to allow writing to
  vanishing states too
* Add unit test for new StateSpaceExplorers
* This should allow for the parallel implementation to re-use the code too
Add tests for including vanishing states in state exploration

* One test fails needs exploring
Remove complicated VanishingExplorer #52

* Implement interface VanishingExplorer without abstract class
  now have OnTheFlyVanishingExplorer which performs on the fly removal
  and a SimpleVanishingExplorer which does not perform any removal
  and just returns the vanishing state

* Added cucumber tests
ReachabilitGraph contains vanishing state inclusion checkbox, #52

* Create relevant VanishingExplorer
Comment up ReachabilityGraph a bit
Comment up State space exploration entirely