replace davclient.js with perry-mitchell/webdav-client

[individual-it]

subtask of #705

the current davclient is not working on node, so we need to replace it with a client that works with node as well as browsers.
one possibility is https://github.com/perry-mitchell/webdav-client
It used not to support customer dav props see perry-mitchell/webdav-client#165 (current status need to be researched and if needed an upstream PR need to be created)

[dpakach]

Fixed by #735