Add base+ images to repo and info to README

[jjbrosnan]

Will require updates to the docs repo.

[devinrsmith]

I think we need to, at a very minimum, have a testing script we run through with each of the compose compositions to make sure it all works. As it stands, I think a large number of them will not work.

In addition, I think we should try and work towards a new strategy instead of having the matrix of python packages and examples/no-examples. We can work to parameterize these compose definitions in the future (using environment variables, or .env files), and it may reduce complexity.

[jjbrosnan]

I have tested every docker-compose file in this PR. They all work. There is one thing to note:

The two NLTK images cause warnings in the web console when starting up Deephaven because a couple of other Python packages aren't installed: tkinter and one other.