RF: Change default patch size to 5 x 5 x 5.
RF: Change default patch size to 5 x 5 x 5.

Addresses https://github.com/nipy/dipy/pull/1223#discussion_r116266756

Also, address: https://github.com/nipy/dipy/pull/1223#discussion_r116264609

FrancoisRheaultUS/dipy,nilgoyyou/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy