Add infrasound and hydrophone channels; known channels list (feature request)

We're seeing requests to archive these channels from mixed PIC and non-PIC equipment experiments. For 201817, I obtained a response by using a channel name that Nexus knew, and then manually changing it back to the correct channel name afterward, but the overall sensitivity and corner frequency were not correctly calculated, so I am not a big fan of this approach.

201951, 201456, and 202033 would like to archive their infrasound data and calculate responses in Nexus. 201951 & 201456 I believe used our DASes and their sensors for part of what they want to archive.

Channels being requested: ?DH ?DF where ?=B,G,H, etc.

I realize adding these channels will be low-priority because PIC equipment involvement is minimal, so I would also like to request an easy-to-access public list of known channels for which Nexus will compute responses, so we and PIs have something definitive to refer to. I also think this list will make it easier to determine if a lack of computed response is a bug or not.

Thanks! Holly

(edited again to correct PIC ID)