[B] Rename Fish to FishHook - Fix BUKKIT-3856

Fish is a badly named class. This change creates the FishHook class for current use and future transitioning to.

To clarify, all further Bukkit changes should be made to FishHook, and all further CB changes should inherit Fish, until it is time to break.

https://bukkit.atlassian.net/browse/BUKKIT-3856