Improve JavaDoc documentation for sampling vs. counter based energy calculations

[cammoore]

Reported by philipmjohnson, Oct 6, 2010
Although WattDepot now supports counter-based energy calculation (with sampling-based backup if counters are not available), the existing JavaDoc documentation does not make that clear.

It would be best to add additional methods for EnergyGenerated and EnergyConsumed that do not have a sampling interval argument at all, which corresponds to the REST API call without the sampling interval that defaults to 1/10 or 1 minute if needed.