A function that takes in either a list of vectors or matrices and computes a weighted average of them, where the weights are applied to every element in the list.
weighted_combine_list(l, w, normalize_weights = TRUE)
matrix or vector corresponding to the weighted average of all of the elements in `l`
a list that contains either vectors or matrices of the same dimension that are to be combined
a vector of weights, the weights should have the same number of elements as `length(l)`
whether or not to force the weights to sum to 1, default is true