[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
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> You can also add a shuffle=True|False option. This would be consistent with SGDClassifier, for instance.
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+1 but first we'd like to be sure it's useful. @mblondel what's your take
on this?