Updating the Eryops model

- Added spawner egg temporarily just for development.

- Fixed the Eryops hitbox.

- increased the positonY of the head1 and head2 boxes of the Eryops
model by 0.1,  in order to fix the overlaping texture glitch.

- Made some constant animation of the tail and head of the Eryops. Very
slow and smoth movement. I think the rotation points of the head is a
little bit off.

- Created the render class for the Eryops model.

- Created a new method in the Modentities class where we can easily
register entities and their spawner eggs. Biome spawns should be done
separately.

- Registered the entity Eryops rendering.

Notes: Toes of the model are
very difficult to animate.
I don't have the vanilla reference yet, so I
haven't done any thing in the EntityEryops class apart from the hitbox.