Add d3js targeted management on the Playground renderer

[juliendorra]

I am testing using D3js with Paysage, and it works quite well (as ProcessingJS leave the Javascript alone. I just have to load the library in my code).
But ProcessingJS needlessly create a canvas and an object with lots of methods, etc.
It might be better to have a dedicated d3js way of running the d3js code.

We could use the mediatype (text/javascript) and client (either programme or d3?) infos to help the Playground renderer handle it better.