Add first version of permutation interence method in the model_selection module.

[LegrandNico]

This is my first trial for this method (contributing to #124 ). The function is not working as expected yet, I think this is due to the way the correlation coefficients are extracted (?). Also, it is not feature-complete (it is not possible to provide permutation idx yet).

[jameschapman19]

This is really nice work!

Sorry for my slowness getting back to you. Had to properly read the MATLAB code to see how it works. Let me know your thoughts on the above. Would be good to try to side-by-side some data with the MATLAB code as a sense check.

[jameschapman19]

A particularly fiddly bit is that the permutations are on the U and V matrices which are subspaces of X and Y.