Pandora's Box

Changes:

• Effects are now registered using a custom registry, the one for Box Effects registers effect classes to be loaded from NBT when the box gets loaded again from NBT, and the one for EffectHolders registers holders which can then have an effect creator defined. Effect creators must be defined for an EffectHolder in order for it to work.

• Added loot to cityscape buildings.

• Reverted water_pool and lava_pool to their old functionality.

• 1.16 soon™

• Fabric... Eventually