[WIP] Subplots support in mpl

OK, this is a basic implementation of subplots support in mpl compat layer.
I used np arrays to setup the geometry to pass to GridPlot.

As a bonus, I have made changes into the file to fit a [template](https://gist.github.com/damianavila/9632346) I have added to the wiki, and I think it would let us arrange the code in a visually ordered way... which will saves us some time in the future. 

If you agree I would like to order all the python code in this way... maybe I can open an issue for the discussion... let me know if you want to discuss it elsewhere.