Update project before possible deprecation

[pavelhoral]

Even though there is issue #4 for deprecating this project, it would be helpful to update it:

• drop unwanted files (empty sites, CC-BY-NC-ND sources, ...)
• update pom.xml (update parent and dependencies)
• add GitHub workflow config
• make the project buildable with JDK 17

Inspiration:

• Upgrade to current wrensec-parent and fix broken build wrends#38
• WrenSecurity/wrensec-script@642296a
• Upgrade master to the current wrensec-parent wrenam#48

[pavelhoral]

I have completely missed the fact that I have already created PR for this very thing :) - #5

[pavelhoral]

I have merged two pending PRs and verified the project build works with JDK 17. I don't think we need to update GH workflow as this project will be merged into wrensec-commons with its own GH workflow.