Support other transports

[btrask]

Currently StrongLink uses plain HTTP (or eventually HTTPS) for everything, including the real-time query results list (which is an abuse of the protocol, since it's intended for documents, not continuous updates). We should eventually support WebSocket for updates and other protocols like BitTorrent for file transfer.

There's a lot of options and the sync system doesn't care, it can work over just about anything.

[btrask]

The new sync implementation makes this close to trivial. You give the SLNSync object a list of URIs, and it tells you which ones it wants and when. Then you get the data for them using whatever protocol you want.