Converted the webdav special remote to the new API. All done with converting everything now!

I also updated the new API to support doing things like reusing the same http connection when removing and checking the presence of chunks.

I've been working on improving the haskell DAV library, in a number of ways that will let me improve the webdav special remote. Including making changes that will let me do connection caching, and improving its API to support streaming content without buffering a whole file in memory.