Lots of changes from the last point in Ripcord

    * Removed Python dependency
    * Relicensed code as MIT (no longer derived from xbee2mqtt.py)
    * Semi-compatible with RF24SensorNet (mainly via RF24NetworkHeader types and MQTT topics
    * Extracted RF24Node types, StringSplit, MQTTWrapper
Abstractions; Removed RF24Node_Config

Implemented IMessageProtocol.h
Implemented IRadioNetwork.h