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.
To explain further: These functions should be doxy-commented in the base class, where it should be explained what they're used for and what can be achieved by overriding them. Then, the individual overrides would just repeat the description, going out of date really easily. So instead they just point to the original class. With multi-level and sometimes even multiple inheritance, this helps folks who don't have an IDE capable of searching for the parent.