Calculates the output of linear basis functions for a given set of inputs
This simply amounts to returning the set of inputs with an extra bias column of ones after the last column in the input set matrix.
FI = gtm_lbf(X)
X - the latent variable sample forming the set of inputs; K-by-L
FI - the matrix of basis functions output values; K-by-(L+1), "+1" for the bias basis
function