Nordic "nRF52840 Dongle" Support

@AkosLukacs just wanted to let you know that your intstructions (and sample .py file) were very helpful :)

>process.env
={
  VERSION: "2v06.10",
  GIT_COMMIT: "9811e3d",
  BOARD: "NRF52840DONGLE",
  FLASH: 1048576, STORAGE: 40960, RAM: 262144,
  SERIAL: "xxx",
  CONSOLE: "Bluetooth",
  MODULES: "Flash,Storage,hea" ... "etworkJS,neopixel",
  EXPTR: 536885592 }