Sparse Fascicle Model

This is a start on an implementation of the model we describe here: 

http://arxiv.org/abs/1411.0721

The main current issue with this is that this will have a local dependency on scikit-learn, because it uses ElasticNet for the fit. How do people feel about that? 
In the examples_index you have this as part of the reconstruction models. But here you do also tracking.
I suggest to separate this tutorial in to two tutorials. One that stops at line 131 which belongs in the reconstruction modes. And one does the whole thing and it goes to the tracking section. Makes sense? I would also advise to use the new tracking API. But this doesn't need to be a priority right now. But add it in your todo list.