Add a convenience function for listing status of each detector in ensembles

[tms-bananaquit]

This should about do it. Would be useful for diagnosing behavior.

class Ensemble:
...
  @property
  def drift_state_dict(self):
  """ The ensemble members' current drift states."""
      return {detector_name : det.drift_state for detector_name, det in self.detectors.items()}
...

[tms-bananaquit]

And for retraining recommendations..

class Ensemble:
...
  @property
  def retraining_recs_dict(self):
  """ The ensemble members' current retraining recommendations."""
      output = {}
      for detector_name, det in self.detectors.items():
            if hasattr(det, 'retraining_recs'):
                  output[detector_name] = det.retraining_recs
      return output
...

I think this could also be a one-liner list comprehension, but this is easier to read.

[tms-bananaquit]

There's probably a better way to implement this abstractly for StreamingEnsemble and BatchEnsemble, that will spit out dicts for properties defined there. retraining_recs is probably the only oddball, as it's not defined in detector.py.

More straightforward (and readable?) to dupe this sort of code for the ones we want, though.