Renamed the SimpleMetering enum to Metering as that's what it is in the Zigbee
Alliance Spec. SimpleMetering seems to come from a NXP document which
isn't complete though and the upstream spec is what matters in the end.
Also adds some cluster ids which are in the Zigbee spec but missing in
the NXP document.
Instead of having 2 methods (setAttribute and addOrUpdateAttribute)
to allow specific cluster implementations to override behavior,
merge them into one, setAttribute, and use standard C++ syntax for
calling a base class implementation.
