Based on #

My Version of the PullRequest https://github.com/SpigotMC/BungeeCord/pull/562 
Originally md_5 stated: 

1) Breaks every existing bungee plugin
   # -> I do not move anything a Plugin could relay on.
2) Crushes performance
   # -> If plugins would implement this on their own performence would crush even more
3) No unit tests
  # -> provided my first unit test, i hope its good enough

Later md_5 stated
1) Yes, unacceptable to break every bungee plugin
# -> No comment needed
2) Using a map which now nests deeper to store each priority, listeners should probably be baked to a flat array, calling getAnnotation on each event call..
#-> done that
3) The unit test should have pass/fail/assert conditions.