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/ntp/TZ.tsx

@@ -474,6 +474,6 @@ export function selectedTimeZone(label: string, format: string) {
 
 export function timeZoneSelectItems() {
   return Object.keys(TIME_ZONES).map(label => (
-    <MenuItem value={label}>{label}</MenuItem>
+    <MenuItem key={label} value={label}>{label}</MenuItem>
   ));
 }