Aging mechanism

Today I have added aging mechanism. Now animals are aging and dying.
There is also mechanism for eating and feeding. If animal do not eat for some period
of time then it dies. Player must feed them. I also tuned graphics of the yard
and added bowing head of hen during eating.

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if blitting on Cocos is just like Pygame, try to blit the below sprites after those above - this will avoid some chickens weirdly walking over the head of anothers...
Sort by y value before drawing is what I always do :)