cleaned up gpio and device code, implemented dummy/dry run mode

lib/GpioPin.php

@@ -154,7 +154,7 @@ class GpioPin
     
     public function sysfsWrite($pin, $file, $value)
     {
-        if ($pin) {
+        if ($pin!==null) {
             $path = "/sys/class/gpio/gpio{$pin}/{$file}";
         } else {
             $path = "/sys/class/gpio/{$file}";