Support file versioning

[tobiasKaminsky]

Like in web UI: allow user to restore a previous version of a specific file.
If approved we need to create an issue for the public server API.

[AndyScherzinger]

Sounds good to me! 👍

[tobiasKaminsky]

Server issue: nextcloud/server#4724

[jospoortvliet]

Merged in the server, coming in 14 btw 🎉

[AndyScherzinger]

Some housekeeping... implemented via #2685, so it'll be part of 3.3 🚀 the upcoming feature release 🎉