The program: stores all animals in a single ArrayList, has appropriate
classes for all animals, displays all the details for any animal,
displays the details of a list of animals, generate a list of animals of
a certain type, displays the food required for a list of animals and
displays a list of all animals from a certain environment. Also, the
main method in Ysj_zoo.java has a while loop, so it doesn't need to run
multiple times to check it meets the success criteria.