make vector types actually vectors so new slice changes in libigl don't complain

[alecjacobson]

Lines like this defining a vector output are actually defining matrices:

EigenDense<npe_Scalar_f> I;
EigenDenseLike<npe_Matrix_f> I;

Change these to:

Eigen::Matrix<npe_Scalar_f,Eigen::Dynamic,1> I;