rework protocols and transform
- remove the picking of channels from the protocol, to avoid creating new protocol each time we need a new channels
- the choice of channels is now done in the transform part defined in each model config file, a list of channels type (e.g. "eeg","eog") or channel names (e.g. "Fpz-Cz") or mix of both (e.g. ["eog","Fpz-Cz"]) can be pass though the transform to select a subset of channel, if nothing is pass to the pick_chan argument, the trasnform by default will pick the "EEG" channels