FIX: eeg ds003645s hed demo

[effigies]

This fixes two issues with eeg_ds003645s_hed_demo identified by the schema validator.

1. electrodes.tsv does not permit a task entity.
2. sub-004/ses-1 EEG files lacked a sidecar. I just copied what was consistent in sub-002/003 into a top-level sidecar.

[VisLab]

Thanks for fixing.... ds003645 on openNeuro validated and it uses task in the electrodes file names. I looked in the spec and see that task now isn't in the filename spec for electrodes. Is this new?

[effigies]

The validator was written more leniently than the spec. I have recently pushed bids-standard/bids-specification#1722, which re-added the run to electrodes to accommodate existing data because it had been mentioned in the spec previously. If it would be useful to re-add task to match existing usage, we could open another PR there as well.

But I would like to go ahead and get this in for the sake of testing anyway. We can re-relax the validator separately, if needed.

[VisLab]

@arnodelorme @dungscout96 This may be an issue for bids-matlab-tools. I have posted sccn/EEG-BIDS#212.