Allow multiple channels for P phase in event & pick plots

[TomWinder]

Is your feature request related to a problem? Please describe.
Currently the event summary plot, and pick plots, are hardcoded to consider only Z-component data for P, and [N,1] & [E,2] data for S. This means if you e.g. add in the OBS hydrophone channel to the P-phase channel mapping it isn't plotted.

Describe the solution you'd like
Allow multiple channels to be plotted for P; use channel-mapping for both P & S to remove hard-coding.

Additional context
Inspired by @shicks-seismo inquiry about incorporating OBS hydrophone data for P-phase onset calculation. (Note that a quick test shows this is successfully being used for onset & location calculation, just not plotted anywhere for easy inspection!)