Factory classes for base organisms

Finished factory classes and methods for base organisms: Animal, Plant,
and Parasite.
Revert "Factory classes for base organisms"

This reverts commit bb593c30243ff2819853edaf1bb1dc33acca979a.
Revert "Revert "Factory classes for base organisms""

This reverts commit da38017c5915cbcf2a1ca94c09739bac3d2731ec.