Create data repositories as part of post-install

[duncdrum]

Currently the app instructs users to create a collection hierarchy manually via INSTALL.txt, which supposes that users go looking for it in the first place. How about creating the expected collections during post-install automatically?

see #121

[brobertson]

Once your multi-repo patch https://github.com/eXist-db/existdb-packageservice/pull/17 is available, I can add a standard server as a repo and then automatically add a text from there.