Interface data storage in PROGMEM (#71)

Adds a webpack plugin to package interface as PROGMEM into a header file in the framework.
Adds a build flag to optionally enable serving from PROGMEM or SPIFFS as required
Adds documentation changes to describe changes

src/main.cpp

@@ -13,7 +13,11 @@ void setup() {
   Serial.begin(SERIAL_BAUD_RATE);
 
   // start the file system (must be done before starting the framework)
+#ifdef ESP32
+  SPIFFS.begin(true);
+#elif defined(ESP8266)
   SPIFFS.begin();
+#endif
 
   // start the framework and demo project
   esp8266React.begin();