Cross validation

This MR adds the following

• Adds cross-validation using a validation set; the best model based on the lowest validation loss is saved automatically now
• Adds trainer, extractor, training script and unit tests for FASNet architecture
• Small change in MCCNN architecture; added a flag for selecting whether to use sigmoid in eval phase.

bob/learn/pytorch/trainers/MCCNNTrainer.py

@@ -345,7 +345,7 @@ class MCCNNTrainer(object):
 
 			# comment it out after debugging
 
-			if epoch>=24
+			if epoch>=24:
 			
 				self.save_model(output_dir, epoch=(epoch+1), iteration=0, losses=losses)