Blockstates Definition / Multi-modeled Blocks

This enables modders to do blockstates definition in MCreator. That is, apply multiple models on one block.
Therefore, the Block Models property of the Visual tab may be replaced.

Modders should be able to do everything they can do about blockstates by editing json, including:

• Applying models per blockstate
• Let the model rotate in X/Y axis by 90 degrees
• Do UV locking if the model is rotated
• Set up random models for one blockstate
• Set up not only variant-type blockstates but also multi-part-type blockstates

Besides, modders should also be allowed to set different bounding boxes per blockstate.

It would be kind of complex so it seems to have to be Blockly-based, similar to the definition of features.

All the things above would be unavailable if a Block Base is set for the block.