Gotify's notification priority is ignored

[ristomatti]

Gotify sets a priority for the notification but there seems to be no handling for this in pushtify-listener.py. The priority levels aren't the same in Gotify as in Pushover, so supporting it would likely need mapping them to ~equivalent ones.

Pushover priority levels are described here https://pushover.net/api#priority but I didn't quickly find what the priority ranges in Gotify are.