WebDAV on GIN

[achilleas-k]

Respective GIN issue: https://gin.g-node.org/G-Node/Info/issues/35

The current plan is to keep WebDAV access disabled while we work on bringing our fork up to date with upstream GOGS. The update will bring file content access through the web API which can serve similar purposes.

In the future, we may provide WebDAV access to repositories using a separate service.