Zwave rollershutter

This fixes/enhances a few things in the zwave binding -:
1) It reverses the rollershutter direction to now be correct as per the standard. It is also possible to reverse the direction using a config parameter (#1060)
2) Added a celcius to fahrenheit conversion. This uses the scale indicator in the zwave frame to work out if conversion is required. (#1190) (https://github.com/cdjackson/HABmin/issues/148)
3) Added a user definable zero so that a small power indication from a power meter doesn't get interpreted as the device being on. (#1193)


couldn't you simply use Math.max() to accomplish this?