* refactor: new helpers/nrf52 dir

* RAK, startOTAUpdate()

src/MeshCore.h

@@ -41,6 +41,7 @@ public:
   virtual void onAfterTransmit() { }
   virtual void reboot() = 0;
   virtual uint8_t getStartupReason() const = 0;
+  virtual bool startOTAUpdate() { return false; }   // not supported
 };
 
 }