LifeSteal Server-side

This update brings some fixes and tweaks, mainly to the gamerule antiHeartDupe:

• Fixes hearts being given regardless of the killed player's health
• Disabled the gamerule for players that are revived using hearts (since a heart is consumed, it is fair that they also give a heart when killed)
• If a killer is at max health, instead of receiving no hearts, they now receive a heart item
• Fixed a bug where if using /withdraw, the hearts received would be stacked