Fix digitizer check params

The peak-finding algorithm for digitizer traces is based on an average trace that takes the first ntrains. This does not work reliably if, for instance in case of a knife-edge, these first trains show no signal.

This MR aims at correcting this, by calculating the average trace of ntrains over the entire run, using an appropriate stride to select evenly spaced train ids.

It also adds the fix axisRange=None that is already included in !117 (closed)