message: fix keras progbar output collision (2)
  ensures that `keras.model.fit()` progbar output is complete before any output from custom callbacks appears on epoch end. Basically this edit puts the standard `ProgbarLogger` first in the list of callbacks. Originally discussed at [tf github](#43184) with problem description and gist examples. Latest example is [here]((https://colab.research.google.com/gist/poedator/3630b1cdec32ff6ef6ccdf6b63c4957a/custom_callback.ipynb).
diff: @@ -264,7 +264,7 @@ class CallbackList(object):
  if self._progbar is None and add_progbar:
  self._progbar = ProgbarLogger(count_mode='steps')
  - self.callbacks.append(self._progbar)
  + self.callbacks.insert(0, self._progbar)
  if self._history is None and add_history:
  self._history = History()
  