Added betweenness centrality #781
Added betweenness centrality #781

Betweenness centrality is added
Small optimizations on closeness centrality

soomin-maeng/cytoscape.js,rlugojr/cytoscape.js,KonstantinShemyak/cytoscape.js,KonstantinShemyak/cytoscape.js,rlugojr/cytoscape.js,soomin-maeng/cytoscape.js