[hackathon] tooling for installing content packages in sling

[Stefan Seifert]

- we currently have 2 "initiatives" - the one from composum, and the one in 
sling that carsten started and konrad picked up later
- we should replace the composum one with the sling one in the sling starter
- work on the sling one is nearly completed, a release can be done soon
- uninstallation: restore line to trigger a new cycle

stefan