This breaks backward compatibility with `maven-site-plugin:3.4.x` and
possibly other old versions as well. A revision bump is recommended.

This commit updates the Maven plugin-related dependencies and modifies any
code affected by breaking changes.

Closes hcoles#1037

This downgrades the `maven-reporting-*` libraries to use the latest
non-milestone version. In addition, the integration tests are updated to use
the latest non-milestone version of `maven-site-plugin`.

Note that the surefire dependencies need to remain on a milestone version to
avoid missing class errors.

Closes hcoles#1037