Add new algo for closeness on undirected graphs.

This code is based on the NetworkAnalyzer plugin used in Cytoscape. For the moment, only closeness centrality has been implemented, but I plan on implementing full network analysis. This implementation is much much faster than the previous one. I will also eventually need to implement a DirectedGraphAnalyzer.
Make computeAll() return closeness.
Update pom.
Fix pom.
Make changes for centrality with all weights 1.
Update pom.
Change fromNode() to baseNode().
Update doc of UndirectedGraphAnalyzer.
Update gitignore.
Make example graph correspond to shp file.
Rewrite BFS using GraphHopper.
Inherit printEdges() from LevelGraphStorage.
Rename Undirected... to Unweighted...
Do some code cleanup.
Refactor from graphhoppersna to graphhopper/sna.
Update pom for OSGi bundle.
Refactor the graph analyzers.
Implement closeness for weighted graphs.
Clean up unit tests for closeness centrality.
Add unit tests for graph analyzers.