Add support for WebDAV

[prabirshrestha]

Would it be possible to have WebDAV support? Currently rclone allows us to serve any remote as WebDAV server which means we can start interacting with backends currently not supported by ccViewer.

[lithium0003]

It sounds good. I'll plan to implement WebDAV backend.

[Jwink3101]

This would be very useful since, as it stands now, the backends themselves are not self-hosted. Any self hosted backend would be appreciated (webDAV, FTP, SFTP, etc)