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

data/config/demoSettings.json

@@ -1,3 +0,0 @@
-{
-  "blink_speed": 100
-}

data/config/mqttSettings.json

@@ -0,0 +1,11 @@
+{
+  "enabled": false,
+  "host": "test.mosquitto.org",
+  "port": 1883,
+  "authenticated": false,
+  "username": "mqttuser",
+  "password": "mqttpassword",
+  "keepAlive": 16,
+  "cleanSession": true,
+  "maxTopicLength": 128
+}