omicron-plot outputs files named "no_trigger" (no the standard naming convention which includes the channel instead) when no trigger is found

When no trigger is found, omicron-plot changes the generic name of the output png files: the fragment normally displaying the input channel is replaced by the string no_trigger. Unless there is a good reason for that, I would suggest keeping the same filename structure regardless of whether triggers are found or not. Use case: when running omicron-plot in a loop to probe a long period of data (day by day for a week; week by week for a run; etc.), that change of filename in case there are no triggers makes more complicated the post processing of the output plots (for instance merging all the png files in a single pdf) as the alphanumerical order is broken.