Do not force mlflow usage

Closes #29 (closed)

dan/manager/training.py

@@ -8,7 +8,6 @@ import sys
 from datetime import date
 from time import time
 
-import mlflow
 import numpy as np
 import torch
 import torch.distributed as dist
@@ -22,9 +21,13 @@ from torch.utils.tensorboard import SummaryWriter
 from tqdm import tqdm
 
 from dan.manager.metrics import MetricManager
-from dan.mlflow import logging_metrics, logging_tags_metrics
 from dan.ocr.utils import LM_ind_to_str
 from dan.schedulers import DropoutScheduler
+try:
+    import mlflow
+    from dan.mlflow import logging_metrics, logging_tags_metrics
+except ImportError:
+    pass
 
 
 class GenericTrainingManager: