channel controller improvements

[bendichter]

I would prefer changing [<][>] to up and down arrows. I think of left/right as through time and up/down as through traces.

It's not clear from this controller how many electrodes there are. Could you add that?

Why have the # electrodes as a dropdown instead of a integer text entry field that only accepts positive integers?

[magland]

The first two items have been implemented.

I'm going to keep the # channels selector as it is because I think the user usually wants to jump to a particular number of channels, and I don't see the need to allow the user the added flexibility of specifying a specific number that is not one of the presets.