Allow NBT on Block/Item Entities

The new Display Entities would be a lot more versatile for map makers and artists if we could set NBT on them based on what Block or Item is being used.

Examples blocks/items being: Banners patterns/colors, Player Heads textures, Armors trims/dyed color for leather armor, Decorated Pots shards, Painting variant, Crossbow projectile, and Maps.

With this change map makers will have an even bigger selection of resources to use for the display entities!