bsuite environment implementation

[RobertTLange]

Implement the set of classic bsuite environments:

• [x] catch.py
• [x] bandit.py
• [x] deep_sea.py
• [x] discounting_chain.py
• [x] memory_chain.py
• [x] mnist.py
• [x] umbrella_chain.py
• [x] cartpole.py - Check if this is different from OpenAI gym version
• [x] mountain_car.py - Check if this is different from OpenAI gym version

[RobertTLange]

CartPole seems to use different hyperparameters/clipping. Leave both gym environments for know in gym style.