Tensorify episodes and labels to save memory and simplify things

[eracah]

Episodes

Before:

• list of lists of pytorch tensors (one tensor for each example)

After:

• list of pytorch tensors (one tensor for each episode)

Labels

Before:

• list of list of dicts (each dict is one example/state)

After:

• list of dicts (one dict for each episode)
• each dict has keys being state variables and values being 1-D tensors of each state variable realization for the episode