Pipeline implementation for BatchGenerator

* Add end_epoch_callback in Trainer
* Fix Layer.ACTIVATION in cas of nn.Module

trainer.py

@@ -99,6 +99,9 @@ class Trainer:
         self.benchmark_step = 0
         self.benchmark_time = time.time()
 
+    def end_epoch_callback(self):
+        pass
+
     def train_step_callback(
             self,
             batch_inputs: torch.Tensor, processed_inputs: torch.Tensor,
@@ -177,6 +180,7 @@ class Trainer:
                     self.benchmark_step += 1
                     self.save_summaries()
                     self.batch_generator_train.next_batch()
+                self.end_epoch_callback()
         except KeyboardInterrupt:
             if self.verbose:
                 print()