Fix channel selection in PowerSupply GUI
In the current code, the GUI selects the wrong channel in the PowerSupply window. Basically it selects the channel having the index corresponding to the channel number.
I'm using a CAEN power supply.
I'm also removing some useless lines, please check.
def addChannel( self, channel)
is called when a new channel is added, so it should be pointless to check if the text is the box is changed.