Enhancement: refactor docs and tutorials

With this PR we move all example configurations out to a dedicated repository,
https://github.com/cs3org/reva-configs, and the tutorials to the Wiki.
We also remove all obsoleted content, and keep the auto-generated doc
on a dedicated folder.

This is to help the community further develop the documentation
and configuration on separate repositories.

https://github.com/cs3org/reva/pull/5185
