Support for custom baby entity models

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Issue description

Hay Klemen, I have been thinking baby entities, and how to fix the current issue where they are always adults.

Would it be possible to have a second .java import for a baby entity model?

This would give the community much needed support for baby entities,
but also give the community more options when it comes to texturing, modeling and adding custom sounds to them.

I know this would be a large project and probably wont make 2020.2,
but I though I would suggest it anyways and see what the community things or has any extra ideas to add to the foundation of this idea.

Issue comments

I know this would be a large project and probably wont make 2020.2,

This is definitely a very far-sighted idea with quite a complex implementation, but I will look into it in the future.

Could you add in the same time the option to reproduce mobs (the food to use) ? (If it's to different, I can open a new ticket.)

Not sure what you mean as this is already possible.

Since this feature is only functional with default and basic entities like cows, pigs, sheeps and so on, i think the best idea is to add an option to make "new baby entity". Works just like a normal entity, it extends that entity but some parameters are Overrided like the pitch of the played sounds, the life percentage, the speed and so on. Models made by the player.