Third, last & double life datapack by CrappyToast

Squashed bugs:
- When just starting out you would immediately die from one hit of damage, this is now fixed.

- Having half a heart of health and then taking damage wouldn't kill you.

Improvements:
- The heart synchronization now only updates when one of the players take damage, this makes it easier for both players to regenerate some health when they are not in combat.

Added:
- Heart synchronization after healing
- reworked death system, so that when you die your soulmate will always die with you as well.