Build a sorted list of unique basis functions based on columns, where each basis function is a list
make_basis_list(X_sub, cols, order_map)A subset of the columns of X, the original design matrix.
An index of the columns that were reduced to by sub-setting.
A vector with length the original unsubsetted matrix X which specifies the smoothness of the function in each covariate.
Note that sorting of columns is performed such that the basis order equals cols.length() and each basis function is a list(cols, cutoffs).