Add http backend

[almarklein]

A backend that runs a webserver that you can connect to with your browser. Multiple clients are supported (eventually).

Using ASGI, so it can run on any ASGI server and we don't have any hard dependencies 🚀

• ASGI server.
• Websocket connection.
• Implement JS to be a AFM (anywidget front-end module) host. Or JS to control the renderview directly.
• Python backend module.
• Support for multiple simultaneous clients.
• Support for including this in a larger web app, e.g. FastAPI.
• Allow customizing the html and e.g. add a logo.
• docs
• Cleanup

---

WIP AFM host code, saving here for reference, but I think I'll skip the afm:

        import {default as afm_factory} from './renderview-afm.js'
        const afm = afm_factory();

        // Open websocket
        const ws = new WebSocket("ws://" + location.host + "/ws");

        ws.onopen = (e) => {


        };
        ws.onerror = (e) =?
        ws.onmessage = (e) => {
            let msg = e.data
            if msg.
        }
        ws.onclose = (e) => {
        }

        const callbacks = {}
        const store = {"css_height"}
        let storeChanges = {}

        class AfmModel {
            on (eventName, callback) {
                callbacks[eventName] |= []
                callbacks[eventName].push(callback)
            }
            get (key) {
                return store[key]
            }
            set (key, value ) {
                store[key] = value
                storeChanges[key] = value
            }
            save_changes () {
                ws.send({'type': 'storeChanges', 'data': storeChanges})
                storeChanges = {}
            }
            send (ob) {
                ws.send(ob)
            }
        }

        const model = AfmModel();
        const el = document.getElementById('canvas')

        afm.initialize({model});
        afm.render({el})

[almarklein]

Progress! You can basically replace one line to say from rendercanvas.http import RenderCanvas, loop, and run the same code, but now its a webserver 🚀

[almarklein]

This is nearly done. Need some cleanup, and resolving some small todos. The server can take multiple clients, who each see the same rendered image. The stream is currently throttled by the slowest connection. Only one client is active: it determines the size of the canvas, and the controls the mouse etc.