Tree Spirit

Added a life extending (when away from the core) item (+12 squashed commit)

Squashed commit:

[c0705e6] Fix grass blocks spreading to blocks that have a block on top of them and not turning to dirt if they ahave a block on top

[ae061a9] Death timers persist across world reloads

[583b964] Remove death timers on player join

[2990131] Fix normal sapling not placing on core

[72ef6d0] Give player sapling on first login

[0ea4d3f] Added recipes

[b48fccf] Add essence drops to mobs and leaves (vanilla and spirit)

[70eb460] Zombies, creepers, and skeletons can attack the core

[78a54ca] Remove cores if they have no owner

[bfcfceb] Added grass blocks

[eb03327] Added dimensional cores