Add switch to suppress 'stale' data

[CharlesGodwin]

The current program generates a device record every time a request is made via getDevices() method is called. But the situation can occur where there has not been any fresh data provided by a device since the last call. The result is that two or more calls to getDevices() will return exactly the same information and give no indication the device has not reported in this interval.

I intend to add a runtime option to allow detection of this 'non-reporting" and suppress a duplicate, stale record. The default behaviour will remain as before.