[MRG] create new plotting.contrib subpackage and add plot_contour_matrix

Create contour matrix plots and optionally animate a cut on one field. This is a nice way to visualize multivariate data.

![out](https://f.cloud.github.com/assets/202816/1144912/4a4ec168-1de0-11e3-910b-2e585d1b8ffc.gif)