Cannot currently write correct metadata from NRL v1 or v2: customizing an NRL response

[rcasey-earthscope]

@metempleton :
I could not currently write correct metadata (with either NRL version), due either to bugs or inappropriate logic if you customize an NRL response (wrong number of poles/zeros and sensitivity issues).

I just finished testing Yasmine to update IM metadata. Outside of documented bugs, it actually
worked - until I customized my responses and had no way to recalculate total sensitivity.
So a user would need to export the XML, run evalresp on it to find the new value, and make
edits. Also, Yasmine validate response amplitudes, and if stage gain frequencies vary, neither
does the stationXML validator. When you put all of this together, it seems like a recipe for a lot
of bad response sensitivities.
Can Yasmine include a sensitivity calculator that handles frequency correctly (rather than just
multiplying stage gains)?

[rcasey-earthscope]

Provided the code can create viable sensitivity values from an NRL instrumentation merge, this would suggest that the evalresp-like code exists, but is not wired to properly trigger when hand edits are done. I thought all of this code was built in to ObsPy, so there might be something in the Yasmine wiring that needs to be added.

[metempleton]

In addition to not being able to recalculate total sensitivity, the problem of not being able to write correct metadata for customized responses is also due to bugs #37 and #40.