If-Modified-Since granularity issue

[jmacauley]

HTTP If-Modified-Since has second level granularity, however, MRML model version has a millisecond granularity. Current code compares If-Modified-Since parameter against a rounded down model version value. This can cause an issue if a new model is received in the same second as the previous model AND the SENSE-O queries the model after the first, but before the second model update is received.

I have added this note to track this issue. I recommend implementing push notifications to address the update issue so polling with If-Modified-Since would no longer be required.