Small Dijkstra refactor for future overriding.

In the near future I plan on overriding updateNeighbor for an
accessibility function that will need access to startNode.
Add AsUndirectedG
Remove unneeded resetNodes().

We do this in the init() function of Dijkstra and BFS every time
calculate(startNode) is called. There is no need to do it twice.
Put the toString() method back
Rename this test appropriately
Add GraphPrep and all possible Dijkstra tests

The new GraphPrep makes it easy to enter a new example graph and
consider all possible orientations of (un)weighted
(un)directed/reversed.

TODO: Make the DijkstraCormenUndirectedStarToStarTest use the
CormenGraphPrep.
Remove ununsed import
Remove all VAccess to fix failing build.
Merge pull request #30 from agouge/update/small-improvements

Several needed improvements:

* Add AsUndirectedG, AsUnweightedG, AsUnweightedDirectedG
* Remove unneeded resetNodes()
* Add GraphPrep to facilitate adding a graph under all possible configurations: (un)weighted (un)directed/reversed
* Add tests for Dijkstra#calculate(startNode) on the Cormen graph using CormenGraphPrep