Make the construction of QLearningAgents easier

[sofian]

It is currently quite cumbersome to create a QLearningAgent (and also to free its memory). Quick example of creation code:

  policy           = Q_NEW(QLearningEGreedyPolicy)(EPSILON);
  actionProperties = Q_NEW(ActionProperties)(DIM_ACTION, N_ACTIONS);
  nn               = Q_NEW(NeuralNetwork)(DIM_OBSERVATION+DIM_ACTION, N_HIDDEN, 1, LEARNING_RATE, DECREASE_CONSTANT, WEIGHT_DECAY, true);
  qFunc            = Q_NEW(QFunction)(nn, DIM_OBSERVATION, actionProperties);
  agent            = Q_NEW(QLearningAgent)(qFunc, policy, DIM_OBSERVATION, actionProperties, LAMBDA, GAMMA);

We could at the very implement a set of utilities to automatically generate the neural network with appropriate dimensions.