Anomaly Detection in Naarad

* User can specify anomaly_detection_metrics for any metric in the config file, to enable anomaly detection for that metric/sub_metric
* Support highlighting of anomaly time period using matplotlib in time series images
* Support highlighting of anomaly time period in client side charting
There are many levels on indentation in this method. Can you do this to reduce the method indentation?

    if len(self.anomaly_detection_metrics) <= 0:
      return