Most of the mFi sensors are able to reasonably provide accurate
readings to a tenth of a unit or so. This patch rounds them for
better display in the UI. Normally, I would expect this to be a view
action instead of altering the actual data emitted, but since these
values are reasonable for sensor precision, we're not really losing
anything. I followed the model from the openweathermap component, which
rounds for readability in the backend.