Integrate fps-webdav with fps-auth and fps-contents

[davidbrochart]

Problem

The fps-webdav plugin has its own authentication and authorization system, separate from e.g. fps-auth.
Also, fps-webdav could play a similar role as fps-contents, with finer-grained permissions (per folder, etc.).

Proposed Solution

I'm not sure how difficult it would be, but it could be interesting to integrate fps-webdav with the rest of Jupyverse.