Animals MAIs: get rid of animal_type= key

The previous value of animal_type= now goes directly into ai_type=
Animals MAIs: add syntax translation and deprecation message

So that the ai_type=animals animal_type=... syntax still works for the
time being.
Animals MAIs: add individual engine macros for each AI

... so that only the code for the animal AI used is loaded.
Add deprecation message for MICRO_AI_ANIMALS macro