Smoke test helper script using Selenium or similar.

As we do not have end-to-end blackbox tests for the whole WebRCA user
experience. Nor for the UI part (excluding Slack). We are prone to errors and
regressions.

The testing part of code review becomes more challenging. Expecially since we
do not have real testers.

Let's create a Selenium script that can be used for (some) basic UI
interactions and lower the probablility of regressions.

The script would be run manually and be available for reviewers (or anyone) who
wants to quickly test some basic functionality in the UI.