Unify UnitAI and AnimalAI.
r8995 / rP8995 (#563) introduced an ANIMAL-state from a separate AnimalAI-component (introduced in r7763 / rP7763).
This patch merges that separate state and brings the ROAMING and FEEDING (renamed to LINGERING) under the INDIVIDUAL.IDLE-state.
This enables e.g. city-building mods to have human units that linger and roam or animals that behave like humans.
The specific values for animals might need tweaking after this.