Replace highcharts by other charting library

[porduna]

We use highcharts.js, a great JavaScript library for generating charts. However, this library is not open source, and therefore we should not use it inside or distribute it as part of this project. We could search and replace the library by any other library, or even pass that task to the server side (rendering it in .jpg or whatever)

[OscarPDR]

We can have a look at this library:
http://nvd3.org/
It's based on the 3djs, but it seems easier to use. The following example shows 2 different escales on the same graph, as we have talk in the hangout:
http://nvd3.org/ghpages/linePlusBar.html
nvd3's licenses are apache + 3djs's one.