Rework backend add MQTT and WebSocket support

* Update back end to add MQTT and WebSocket support
* Update demo project to demonstrate MQTT and WebSockets
* Update documentation to describe newly added and modified functionallity
* Introduce separate MQTT pub/sub, HTTP get/post and WebSocket rx/tx classes
* Significant reanaming - more accurate class names
* Use PROGMEM_WWW as default
* Update README documenting PROGMEM_WWW as default
* Update README with API changes

interface/src/components/WebSocketController.tsx

@@ -0,0 +1,133 @@
+import React from 'react';
+import Sockette from 'sockette';
+import throttle from 'lodash/throttle';
+import { withSnackbar, WithSnackbarProps } from 'notistack';
+
+import { addAccessTokenParameter } from '../authentication';
+import { extractEventValue } from '.';
+
+export interface WebSocketControllerProps<D> extends WithSnackbarProps {
+  handleValueChange: (name: keyof D) => (event: React.ChangeEvent<HTMLInputElement>) => void;
+
+  setData: (data: D, callback?: () => void) => void;
+  saveData: () => void;
+  saveDataAndClear(): () => void;
+
+  connected: boolean;
+  data?: D;
+}
+
+interface WebSocketControllerState<D> {
+  ws: Sockette;
+  connected: boolean;
+  clientId?: string;
+  data?: D;
+}
+
+enum WebSocketMessageType {
+  ID = "id",
+  PAYLOAD = "payload"
+}
+
+interface WebSocketIdMessage {
+  type: typeof WebSocketMessageType.ID;
+  id: string;
+}
+
+interface WebSocketPayloadMessage<D> {
+  type: typeof WebSocketMessageType.PAYLOAD;
+  origin_id: string;
+  payload: D;
+}
+
+export type WebSocketMessage<D> = WebSocketIdMessage | WebSocketPayloadMessage<D>;
+
+export function webSocketController<D, P extends WebSocketControllerProps<D>>(wsUrl: string, wsThrottle: number, WebSocketController: React.ComponentType<P & WebSocketControllerProps<D>>) {
+  return withSnackbar(
+    class extends React.Component<Omit<P, keyof WebSocketControllerProps<D>> & WithSnackbarProps, WebSocketControllerState<D>> {
+      constructor(props: Omit<P, keyof WebSocketControllerProps<D>> & WithSnackbarProps) {
+        super(props);
+        this.state = {
+          ws: new Sockette(addAccessTokenParameter(wsUrl), {
+            onmessage: this.onMessage,
+            onopen: this.onOpen,
+            onclose: this.onClose,
+          }),
+          connected: false
+        }
+      }
+
+      componentWillUnmount() {
+        this.state.ws.close();
+      }
+
+      onMessage = (event: MessageEvent) => {
+        const rawData = event.data;
+        if (typeof rawData === 'string' || rawData instanceof String) {
+          this.handleMessage(JSON.parse(rawData as string) as WebSocketMessage<D>);
+        }
+      }
+
+      handleMessage = (message: WebSocketMessage<D>) => {
+        switch (message.type) {
+          case WebSocketMessageType.ID:
+            this.setState({ clientId: message.id });
+            break;
+          case WebSocketMessageType.PAYLOAD:
+            const { clientId, data } = this.state;
+            if (clientId && (!data || clientId !== message.origin_id)) {
+              this.setState(
+                { data: message.payload }
+              );
+            }
+            break;
+        }
+      }
+
+      onOpen = () => {
+        this.setState({ connected: true });
+      }
+
+      onClose = () => {
+        this.setState({ connected: false, clientId: undefined, data: undefined });
+      }
+
+      setData = (data: D, callback?: () => void) => {
+        this.setState({ data }, callback);
+      }
+
+      saveData = throttle(() => {
+        const { ws, connected, data } = this.state;
+        if (connected) {
+          ws.json(data);
+        }
+      }, wsThrottle);
+
+      saveDataAndClear = throttle(() => {
+        const { ws, connected, data } = this.state;
+        if (connected) {
+          this.setState({
+            data: undefined
+          }, () => ws.json(data));
+        }
+      }, wsThrottle);
+
+      handleValueChange = (name: keyof D) => (event: React.ChangeEvent<HTMLInputElement>) => {
+        const data = { ...this.state.data!, [name]: extractEventValue(event) };
+        this.setState({ data });
+      }
+
+      render() {
+        return <WebSocketController
+          handleValueChange={this.handleValueChange}
+          setData={this.setData}
+          saveData={this.saveData}
+          saveDataAndClear={this.saveDataAndClear}
+          connected={this.state.connected}
+          data={this.state.data}
+          {...this.props as P}
+        />;
+      }
+
+    });
+}