PPO Critic

[MagMueller]

@leikun-starting Thank you very much!

I have some questions in regard to the critic, maybe from there some improvements arise.

• Currently the critic only receives the job embedding and not the machine embedding
• Why are you not updating the critic separately, e.g. with the job_v_loss
  job_v_loss = self.MSE(val[j], rewards_all_env[j])
  currently you simply add the critic loss to the actor loss.
• The critic is used in both loss functions (job and machine)