Item Cooldown Handling

[CamperSamu]

For now item cooldowns are handled the vanilla way for Commander Items and per-block with Lectern Commanders.
This can be limiting because if two Commander Items share the same item they both go on cooldown but it makes handling cooldowns way easier.
The solution would be creating an Item Tracker and tracking everything with a player-itemstack pair and a cooldown handler, but it's way less elegant.
I am open to suggestions on this.