mxboard should be optional

[jwmueller]

mxboard should either be optional or it should be explicitly listed as a requirement in setup.py (I vote for the former choice).

It's annoying to keep getting: ModuleNotFoundError: No module named 'mxboard' after import autogluon on new instances because I forgot to install mxboard manually myself.

[cgraywang]

it should already be optional, I think by changing the visualize to none it won't require mxboard.

[jwmueller]

well then shouldn't visualize set itself automatically based on whether try: import mxboard fails or not?

[cgraywang]

yes, we could do this as well, but we should at the same time raise a warning informing the user that the mxboard is not installed yet

[jwmueller]

visualize argument still needs documentation to describe how it can be used, and what (if anything) the user needs to have installed when using visualize