BW, TEST: Rename dipy.sims.tests.test_voxel functions according to changes at dipy.sims.voxel. Adding test for testing kurtosis_elements optional inputs. Remove test_dki which is useless
BW, TEST: Rename dipy.sims.tests.test_voxel functions according to changes at dipy.sims.voxel. Adding test for testing kurtosis_elements optional inputs. Remove test_dki which is useless

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