D3ify and Transitions

Based on https://github.com/alangrafu/radar-chart-d3/pull/18

New features

- d3 style reusable chart api
- switches to selectively disable parts of the chart
- add transitions

See commit messages for more detail.

[![Radar Example](http://bl.ocks.org/tpreusse/raw/2bc99d74a461b8c0acb1/thumbnail.png)](http://bl.ocks.org/tpreusse/2bc99d74a461b8c0acb1)

Background of changes:
I had to implement a visualisation which displays 195 radar charts on one page. It was unfeasible to create 195 svg so I created an interface to allow drawing a radar chart into a svg group. Also I fixed up the `d3.selectAll`'s to match existing elements and only update / redraw changes. Additionally added feature switches to disable unneeded elements (major performance gain) and for sunday entertainment added transitions.

You can see the finished vis here:
http://www.nzz.ch/aktuell/startseite/sommerserie-der-breite-wohlstand-als-thema-interaktive-datenvisualisierung-1.18341500