idea: Establish odav

[Xuanwo]

I used to think that using oay as the sole entry point for webdav, fuse, and s3 was a good idea. However, it turns out we were moving too quickly. We spent too much time figuring out the layout of oay rather than focusing on actual features.

I believe it's time to create odav to consolidate all webdav-related features into a single binary instead. So users who intereseted in webdav can use odav directly.