[WIP] Random coordinate descent

This is just an attempt to check if shuffling of features helps in random convergence, for now it is just a quick hack, if there is really a decrease in the number of iterations, we can shift to the Cython version to reduce the overhead

ping @ogrisel @agramfort
@larsmans What is the correct way to define an unsigned 32 bit integer in Cython here? `f_shuffle` contains feature indices.