parameter scale_by = "normalize" behavior

[aakash10gupta]

In order to scale seismograms so that they are visible on record sections, the parameter scale_by = "normalize" is used so that each seismogram's absolute amplitude is scaled to 1. This does not preserve relative amplitudes of seismograms across stations. In the special case where two sets of seismograms are plotted against each other, there might be a need to "normalize" the two seismograms at each station equally so that the relative amplitudes are maintained at each station, though not across stations. So one set of seismograms will be scaled to 1 while the other set will be scaled equally as the corresponding seismograms from the first set. These scaling factors will likely differ across stations unlike the "global_norm". So, a new option will need to be added for the parameter scale_by to enable this.