make sure optimizer and scaler is reloaded on resume for training diffusion prior script, move argparse to click

dalle2_pytorch/train.py

@@ -117,7 +117,7 @@ def load_diffusion_model(dprior_path, device):
     # Load state dict from saved model
     diffusion_prior.load_state_dict(loaded_obj['model'])
 
-    return diffusion_prior
+    return diffusion_prior, loaded_obj
 
 def save_diffusion_model(save_path, model, optimizer, scaler, config, image_embed_dim):
     # Saving State Dict