This alignes the OnOff cluster with the LevelControl cluster in terms
of signal behavior: Previously, the OnOff cluster would fire a generic
commandSent() signal for some commands and specific signals for others.
Effectively forcing the user to connect multiple signals even if only
the command would be of interest.
The LevelControl cluster instead always fired a generic commandSent()
signal and *additionally* more specific signals for parsed parameters.
This changes the OnOff cluster to be in line with the LevelCluster
as and making the API a bit simpler to use when parameters are not of
interest.
Also it completes the specific parsing for all 3 clusters.
