Added Dataset Cut for Line Chart

Hi, I added two parameters to LineChart to cut each dataSet with a rectangle, like on the picture.

First one is a boolean, second one is an object (w,h,y,x).

![Capture d e cran 2013-03-19 a 10 55 47](https://f.cloud.github.com/assets/2417908/275049/3d5a6c52-907b-11e2-9d20-bfb5bf4c6b4d.png)