Update color system and sheep coloring

[BenCheung0422]

This depends on #437 due to a fix of stackable item interaction on entities

The current color system is pretty lack in customization and content, so this pull request complements and updates these parts.

• As sheep only has white wools, colored sheep is now available in natural spawn.
• There is now small chance in spawning colored sheep.
• Sheep and beds are now colorable.
• Dyes are added.
• 16 colors are implemented in dyes, wools, and colorable items and furniture.
• Adds a new recipe - string * 3 -> white wool * 1
• Adds 19 new flowers replacing original flowers.

When we have biomes supported, different biomes can have different ranges of flower variants generated.

(Discord thread: https://discordapp.com/channels/280723930942013440/1083334895763456072)