Support /io/share[/path/to/file/or/folder] with Web Torrent hosting

We need to allow a user to easily move their data between browsers over the network. We can use https://webtorrent.io/ to provide the ability to upload your filesystem (or whatever portion thereof you specify via URL) into a torrent, and then give a URL (torrent magnet url) others can use to download this filesystem into their browser.

Step 1 of this bug is to do the seeding and upload. We'll have to sort out what *using* that URL looks like, so you get the data installed properly in a new browser.