Populate detector data

[justinvasel]

As of opening this issue, snews/data/detectors only has one detector entry (super-k.json). We want one for each SNEWS detector.

[jpkneller]

Astropy has similar data classes for the detectors - the data was supplied by SNEWS - that we use in EMEWS to compute the path taken by a neutrino through the Earth when we compute the Earth-Matter effect. See this example of what we need.

https://github.com/SNEWS2/EMEWS/blob/main/EMEWS_example.py

How does the data in these detector classes compare with those in Astropy? Can we use these new classes instead of the Astropy ones?