Chooses up to two channels to plot after a config load.
Keeps channels from the previous selection that are still enabled, then fills up to two from enabledChannels in config order.
enabledChannels
channels_enabled from the config.
channels_enabled
Optional
Selection before the reload, if any.
A new set with at most two channels.
Chooses up to two channels to plot after a config load.
Keeps channels from the previous selection that are still enabled, then fills up to two from
enabledChannelsin config order.