Simplified the way Chickens are handled in the hatchery

- Chickens can be picked up
- Chickens can be dropped on claimed tiles
- Chickens leave hatchery only when dropped outside
- Chickens can live 30 turns outside the hatchery. After that, they die
- Only creatures using the hatchery will consider eating a chicken in the hatchery
- A creature not using the hatchery will consider eating chickens outside the hatchery only. Any creature, even ennemy can eat a free chicken
fixes #216