npix - enable high pass filtering when loading waveforms from raw binary

[LaurenzMuessig]

should really high pass filter (and CAR) the raw data when loading from an unprocessed binary. CAR is straightfoward as can be done within snipppet when getting the data from memmap, but high pass filtering needs to be done across full data set. Prob easiest to steal the code from KS, as fairly fast and also enables GPU usage if you happen to have one. This is a bigger job and slightly obsolete as now you probably use the drift corrected file