Correct tint for blocks #25

Block tint depends on the type of block and for some blocks on the biome. The correct colors for each combinations are listed here: https://minecraft.gamepedia.com/Tint

Tint is currently hardcoded to plain grass green for blocks: https://github.com/PrismarineJS/prismarine-viewer/blob/master/viewer/lib/models.js#L232

And to ocean blue for water: https://github.com/PrismarineJS/prismarine-viewer/blob/master/viewer/lib/models.js#L106