Make builtin/generated use tint idexes.

Make "builtin/generated" use tint indexes, right now we can only use tint index 0 if it's a leather item, and we can only use one color.

I would be awesome being able to use tint indexes in any item, and being able to use multiple colors.

It would require making display:{color:0} an array so that we can define multiple colors and those are then used in the model tint index to color our items.
It would help massively in the creation of custom maps or severs, making it a lot faster, players would be able to customize their tools, for example creating a red and yellow sword.