Ploneconf2020 sprint report out for unified installer

@jensens created a new branch of the unified installer that fixes many issues and (coolest part) automatically builds the installer as an artifact. I tested it on Ubuntu 20.04 LTS and on macOS 10.15.7. On Windows there are still some issues. Next step is to update it for Plone 5.2.3 and release it officially and keep working on the Windows fixes.

See the full sprint Google Doc

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