Process SuperKamiokande Neutrino events

[martinjohndyer]

Just as #35 was closed (in #53) we have a new source of alerts - neutrino bursts from supernovae detected by Super-Kamiokande (https://gcn.gsfc.nasa.gov/sk_sn.html). These will be very rare events, but it would be good to add them in at a high priority just in case one goes off while GOTO is observing.