Render items

[leMaik]

There are different types of items:

• [ ] Simple minecraft:item/generated items (added by #1704)
• [ ] Multi-layer minecraft:item/generated items, eg. diamond_leggings_emerald_trim
• [ ] Conditional item models, eg. diamond_leggings
• [ ] Items that use the block model, which could be implemented once #1693 is done

The items can be used in different places:

• [ ] Campfire (added by #1704)
• [ ] Item frames (#790)
• [ ] Display entities (#1691)
• [ ] Items held by players (#1437)
• [ ] Items held by armor stands (#669)