Dht22 and humidity sensor fixed
- after several attempts to do directly from java (via Pi4j - too slow,
  via mmap - java implementation attempts to truncate the underlying
  file, which is not allowed for /dev/mem), I gave up
- so done simply via JNI in the end, using the Adafruit source c files,
  just added an internal loop inside the c code called via JNI, so that
  up to 10 attempts are done if failure ocurrs...
- added all c source files (even though not build through maven, just if
  would need to be changed later), added together with the commands to
  build the shared lib via gcc (on RasPi directly)
- added nativeUtils to avoid any need to install anything manually on he
  box (the app will handle itself)