Refactor NodeBetweennessInfo to (un)weighted.

Also rename PathLengthData variables:
    * distance -> steps
    * distanceDouble -> distance
Refactor PriorityQueue initialization.
Update Dijkstra documentation.
Refactor getAveragePathLength for (un)weighted.
Finish WeightedGraphAnalyzer.

Added DijkstraForCentrality, which extends Dijkstra and can be
used for the betweenness and closeness centrality calculation
in WeightedGraphAnalyzer.
Refactor result printing methods.
Suppress debugging output.
Refactor tests.
Major test refactoring.