Tidy up server and main code.

The server app is now in a new Server module, alongside some launcher code
factored out of the main code.
Fix typo in loader handler.
Move server assets into server directory.
Ignore FUSE crap.
Various item loading fixes and duct tape.
WebSockets are go.

bra now sends model updates on its /stream URL to WebSocket clients,
provided that they upgrade from HTTP to WebSocket; otherwise they
will be served a normal HTTP stream.

The API inspector now shows a WebSocket-based update console, if
viewed with a JavaScript and WebSockets-enabled browser.

There have been some assorted bugfixes, too.