Add basic sack util

[no changelog]

src/main/kotlin/events/ChestInventoryUpdateEvent.kt

@@ -0,0 +1,11 @@
+package moe.nea.firmament.events
+
+import net.minecraft.item.ItemStack
+import moe.nea.firmament.util.MC
+
+sealed class ChestInventoryUpdateEvent : FirmamentEvent() {
+	companion object : FirmamentEventBus<ChestInventoryUpdateEvent>()
+	data class Single(val slot: Int, val stack: ItemStack) : ChestInventoryUpdateEvent()
+	data class Multi(val contents: List<ItemStack>) : ChestInventoryUpdateEvent()
+	val inventory = MC.screen
+}