Initial example of a multi-user Selenium test, in Python

The Selenium test (using unit test framework for convenience) opens two additional windows using JavaScript, then switches among them checking the title of each one. At shutdown it closes all three windows cleanly. The test runs and passes at the command line. This is an initial proof of concept and more interesting tests will be added later.

I also updated the README to help with the details of setting up on a fresh Ubuntu install, and for help setting up chromium-chromedriver when installing it using the apt package manager.