- added a Graph implementation of an AbstractSearchProblem and a first example Example1 illustrating the use of Graph, depth-first, breadth-first, uniform-cost and A*
- added OpenListInterface, Abstract-, Fifo-, Lifo-, and PriorityQueueOpenList; there is now only 1 generic search algorithm
- renamed SearchProblem -> AbstractSearchProblem
- added ClosedListTest