Extending KernelDataset to account for using channels from nearby station as local channels

[kujaku11]

Occasionally a local channel goes down and to get a full transfer function you can use data from a nearby station that was running at the same time. Typically this works better if its the horizontal magnetic channels, but could work for output channels if the stations are close enough. It would be nice if the KernelDataset could account for this.

Perhaps some sort of mapping per channel. Like ex: (mth5_file_path, station, run, ex).