This removes the empty separate files for the different groups and adds
a single file giving short explanations for each group and what to
expect from those groups.
The UI tests now use the latest edition by default. Testing on older
editions should almost never be necessary, so I don't see a need to
document this.
This reformats all the internal docs, so that the md files use at most
80 characters per line. This is the usual formatting of md files. We
allow 120 chars per line in CI though.