Save trigger channel from WAV file

Context

After more reading, I realized the filtering code for DarkSide uses the trigger data, so it should be saved in the Event along with the signal data.

Summary

When reading the file, all channels will be added to the Event object. If the data is LFoundry data (files starting with LF_TILE), the channels are reversed so the signal is still the first channel.

The pulse finders used for this data will need to take into account that only the first channel is for the signal. We might have to make some adjustments or add features later on, but this should become more clear once the filters and pulse finders are being written.

I also added some error handling and made the wav file and directory names more specific by adding lngs like it's called in the sipmfilter Repository.

How was this tested?

Ran with vanwftk and event stepper for ds-wav.json. For both types of files (FBK and LFoundry), the output should be like this with the signal in ch0 and the trigger in ch1: