Name change and cleanup
Name change and cleanup

Changed the name of `_fourier_transform` to `_fourier_modulus`; `dt` does not need to be passed to the function, as it is already included in the Lightcurve object.
StingraySoftware/stingray,evandromr/stingray,dhuppenkothen/stingray,abigailStev/stingray,pabell/stingray