In addition to a label constructed form the combination of site and
measurment type, channels had a name that was specified on creation.
This proven to be not particularly useful (there only being one instance
of the name being set to something materially different from the label);
and this has lead to channels being inconsistenly referenced (some times
a channel is identified by its label, and sometimes by the name).
This commit removes the name from __init__ arguments, and
InstrumentChannel.name is now an alias for InstrumentChannel.label.
