#99 New MED data

Added a new, small (< 0.5 MB) dataset for the MED file format. This new dataset contains data with gaps as well as channels with multiple sampling frequencies.

Hi @dancrepeau1! Thanks for providing the new dataset and adding it directly in git-annex. I added one commit to lock the files to not have duplicates when downloading the file content. Not really relevant for this PR since the files are small, but a good practice for larger files.