Replace pearls with player heads

[squareblob]

(#51) Sadly player heads do not glow... https://bugs.mojang.com/browse/MC-100947

Changes

• removed references to pearls.free_by_throwing
• changed all references to lored exile pearls into lored player heads, except in four cases where both PLAYER_HEAD's and ENDER_PEARL's are checked for the purposes of migration:
  • CoreLoreGenerator::getValidLore
  • BlockHolder::holderVerifyResult
  • PlayerListener::onInventoryOpen
  • PlayerListener::validatePearl

I tested migrating pearls, decaying pearls, repairing pearls, and /ep commands. Everything appeared to work -- though with so many small changes I still may have broken something painstakingly obvious :/.

[Maxopoly]

I'll merge this the next time I'm around for a restart to make sure it actually migrate all pearls properly