BW: Replace design_matrix function with dki_design_matrix implemented on dipy.sims.voxel
BW: Replace design_matrix function with dki_design_matrix implemented on dipy.sims.voxel

oesteban/dipy,villalonreina/dipy,matthieudumont/dipy,sinkpoint/dipy,JohnGriffiths/dipy,oesteban/dipy,matthieudumont/dipy,demianw/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,demianw/dipy,jyeatman/dipy,jyeatman/dipy,StongeEtienne/dipy,StongeEtienne/dipy,nilgoyyou/dipy,FrancoisRheaultUS/dipy,villalonreina/dipy,sinkpoint/dipy,JohnGriffiths/dipy