2 new experience replays: PrioritizedExperienceReplay and NStepExperienceReplay
Added DoubleStateActionRewardStateActionNeuralNetwork and DoubleExpectedStateActionRewardStateActionNeuralNetwork
Renamed ExperienceReplay to UniformExperienceReplay
ExperienceReplays now have their own category.
Refactored the reinforcement learning neural network codes for better mantainability.