Completing SB3 logger metrics to match Visdom & dump SB3 logger in JSON

[pierrot-lc]

Feats:

• Removed the Visdom logfile (--log_file is gone).
• Automatically dump the metrics from the SB3 logger to a json file named progress.json in the experiment directory.
• Add missing metrics to the logger compared to Visdom (the one that came from the agent_validator).
• Add two new metrics: stability and monotony, which are displayed as an example in the ratio_stability and ratio_monotony curves on Visdom.
• Catch cuda OOM during benchmarks and record that event.

Fixs:

• Typo in args.py (average -> avg).
• Device assignment when using avg pooling layer.