Render items

[leMaik]

There are different types of items:

• Simple minecraft:item/generated items (added by Render campfire items #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 Add block display support. #1693 is done

The items can be used in different places:

• Campfire (added by Render campfire items #1704)
• Item frames (Add item frames #790)
• Display entities (Display entities #1691)
• Items held by players (Render blocks and items held by players #1437)
• Items held by armor stands (Render blocks and items held by armor stands #669)