Simple XP Config

adds the ability to configure block xp drops

edit world/serverconfig/blockxpdrops.json

note: only integer block state properties are supported

rerelease: fix mixin crash

example: 

[

{
  "blocks": ["minecraft:nether_wart"],
  "amount": 3,
  "state": {
    "age": 3
  },

 "chance": 0.50
}
]