WIP: Tutorial IPython notebook

First attempt of converting the tutorial to an IPython notebook (as discussed here https://github.com/mne-tools/mne-python/issues/406#issuecomment-12708425 )

As a long term solution it would be very neat if we could have the tutorial as an IPython notebook which gets automatically executed and converted to .rst when the website is built. This would make it much easier to modify the tutorial and would ensure that it actually works (we could probably also include it on doc tests). Also, people could download the `*.ipynb` file and play around with it.

I also did an experiment and added the connectivity estimation with circle plot, but on my machine the plot is messed up (shown twice). We can remove that.