In .cc files please change return value of {{bool set...(...)}} functions to void if they can't return false

Some set... functions in .cc files have the return type bool, some have void. Some throw an error if the position where the object should be set in a vector is invalid, some return false. Sometimes the returned bool is checked whether it's true or false. Some functions, like e.g. Spectra::setSpectrum return bool even though they cannot return false but throw an error instead. Please make all this consistent.