Beds still use the block entity for special rendering, rather than block models

As of 17w47a, each bed color got their own block id (COLOR_bed) with this change, the bed no longer needs to base it's texture/model on any nbt data, as such the the beds can use normal block models again, instead of requiring a block entity and rendering like an entity.

A direct result of this issue is that the side of beds is no longer completely retextureable, as opposed to versions prior to 1.12 and the other editions of Minecraft.