Integrate with sprite-gen

[erlend-sh]

We'd like to try use the sprite-gen project in order to generate creature sprites.

• integrate Evoli with sprite (we can temporarily operate with a fork of sprite if the library needs updating in order to work)
• assign existing creatures to a sprite generated creature. Can be the same one every time, or a different one every time

Related to #25

[erlend-sh]

Closed as a result of our new 3D direction: https://community.amethyst.rs/t/evoli-art-direction/773/2?u=erlend_sh