Make lootchance item specific

[ErikOverflow]

Is your feature request related to a problem? Please describe.
Current lootrate is attached to the enemy's general droprate. The lootrate should still be configurable on a per-enemy basis, but it should be item specific.

Describe the solution you'd like
Combine both the item and the loot rate into a struct on the CharacterLoot class. Hold an array of LootStructs, rather than just an array of Items.

Additional context
Will require modifications to CharacterLoot.cs and EnemyTemplate.cs. May require changes to EnemyHook.cs