Constrained Spherical Deconvolution and the Spherical Deconvolution Transform

This is ready to merge according to my view. It is the code that we used for the ISBI competition. I have added an example for CSD using real datasets. Let me know what you think @stefanv, @MrBago, @arokem, @ecaruyer. We will soon add another tutorial with @mdesco for the SDT. But that will come in a new PR.  We need to expose our API more. Small simple examples will be beneficial. Try to get used to adding an example with any significant source contribution. GGT!