Add aesthetic scorer reward function

ddpo_pytorch/assets/simple_animals.txt

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+cat
+dog
+horse
+monkey
+rabbit
+zebra
+spider
+bird
+sheep
+deer
+cow
+goat
+lion
+tiger
+bear
+raccoon
+fox
+wolf
+lizard
+beetle
+ant
+butterfly
+fish
+shark
+whale
+dolphin
+squirrel
+mouse
+rat
+snake
+turtle
+frog
+chicken
+duck
+goose
+bee
+pig
+turkey
+fly
+llama
+camel
+bat
+gorilla
+hedgehog
+kangaroo