Restructure and tweak drowning

Replaced On...LiquidEvents with On...BlockEvents.
Add prefab component for breathability
Remove missed junk; Rename for clarity;
Simplify the OnEnterBlockEvent

Likely other things that care about location of the block will be better
served by using the MovedEvent
Checkstyle fix
Performance improvements
Merge pull request #772 from Josharias/DrowingToCore#651

Drowning #651