. Removing the "implements Constants" as it is a bad pattern. Interfaces
  should represent types. It also makes the UML diagrams very hard
  to follow. We're just going to use the fully qualified GraphConstants.{x}
  idiom.

. Added the Graphable interface to allow any arbitrary object to be
  manipulated like a vertex in a graph.

. Added a util package that has a dependency resolver that uses a depth first
  search to sort the dependencies for a set of objects that implement
  the Graphable interface. The resolver also works with Strings and
  lists and deps stated as lists of strings so I can resuse the test
  I wrote for the DependencyEngine in jjar.