Improves Tune Jupyter notebook experience by modifying the `JupyterNotebookReporter` in two ways:
* Previously, the `overwrite` flag controlled whether the entire cell would be overwritten with the updated table. This caused all the other logs to be cleared. Now, we use IPython display handle functionality to create a table at the top of the cell and update only that, preserving the rest of the output. The `overwrite` flag now controls whether the cell output *prior* to the initialization of `JupyterNotebookReporter` is overwritten or not.
* The Ray Client detection was not working unless the user specifically passed a `JupyterNotebookReporter` as the `progress_reporter`. Now, the default value allows for correct detection of the enviroment while running Ray Client.
Furthermore, the progress reporter detection logic in `rllib/train.py` has been replaced to make use of the `detect_reporter` function for consistency with Tune (the sign in the overwrite condition was similarly flipped).
Fix CQL getting stuck when deprecated timesteps_per_iteration is used (use min_train_timesteps_per_reporting instead).
CQL does not perform sampling timesteps and the deprecated timesteps_per_iteration is automatically translated into the new min_sample_timesteps_per_reporting, but should be translated (only for CQL and other purely offline RL algos) into min_train_timesteps_per_reporting.
If timesteps_per_iteration, CQL lever leaves the first iteration as it thinks it's not done yet (sample timesteps always remain at 0).
Lint was still failing (but only caught with doctest):
```
File "../../python/ray/rllib/utils/numpy.py", line ?, in default
Failed example:
tree.traverse(make_action_immutable, d, top_down=False)
Exception raised:
Traceback (most recent call last):
File "/opt/miniconda/lib/python3.6/doctest.py", line 1330, in __run
compileflags, 1), test.globs)
File "<doctest default[4]>", line 1, in <module>
tree.traverse(make_action_immutable, d, top_down=False)
NameError: name 'make_action_immutable' is not defined
```
