Animal terrain finisher

Adds animals to cChunkDesc entity list on chunk generation.

resolves #1595 

Note: animals do not spawn, either the list does not get refreshed and sent to world, or the mobs spawn too far away and are removed shortly after.
This is not a good candidate for doxy-comment, it's just a note about where the original function comes from, it doesn't explain what it does. This comment should use regular C++ comment style (`//`)