Change Soul Crystal health modifier to be static instead of percentage based

[noolaan]

This change would work well if a mod/modpack was to change the default number of hearts.

[Aizistral]

Percentage is intended here specifically because of the mods that might change the amount of health a player has. So, if some mod out there gives them +20 HP for a total of 40, each soul crystal should represent 2 hearts instead of one. In this way, crystal loss cannot be overcome or made insignificant with just some health upgrades. This also avoids the issue of where and how to set the limit for how many crystals a player may lose, which becomes rather complex if each crystal stands for a fixed amount of health, and the total health is dynamic.