[unused] Remove NodeList
[enh] Use d3 functions to compute max, mean, sum...
[fix] remove 'undefined' css class and unused code
[fix] Use d3.scale to define Category graphs
[fix] Ignore .DS_Store files
[fix] remove pointer-events for links (and unused events)
Merge pull request #27 from Cynddl/master



Clean d3graph.js code:

    remove unused code;
    use d3.js functions to sort, compute mean, max…
    fix css class for nodes without family or category.

Fix issue #25 and more…