Add pheno004 example dataset

[ericearl]

Meant for the resolution of bids-spec PR 2044. This is a dataset containing a mismatch of subjects with MRI data and tabular phenotypic data to be considered a whole dataset of participants for the sake of the participants.tsv file.

[effigies]

Perfect. Once bids-standard/bids-specification#2044 is merged and the schema incorporated into the dev validator, we can revert the BIDS_SCHEMA and merge this.

[Remi-Gau]

this is leading top some failures on the bids website

https://readthedocs.org/projects/bids-website/builds/27369885/

python data/datasets/examples/tools/print_dataset_listing.py docs/datasets/examples.md
Traceback (most recent call last):
  File "/home/docs/checkouts/readthedocs.org/user_builds/bids-website/checkouts/629/data/datasets/examples/tools/print_dataset_listing.py", line 185, in <module>
    main()
  File "/home/docs/checkouts/readthedocs.org/user_builds/bids-website/checkouts/629/data/datasets/examples/tools/print_dataset_listing.py", line 65, in main
    check_missing_folders(df, root)
  File "/home/docs/checkouts/readthedocs.org/user_builds/bids-website/checkouts/629/data/datasets/examples/tools/print_dataset_listing.py", line 85, in check_missing_folders
    raise ValueError(
ValueError: Found 84 folders but 83 datasets in the table:missing {'pheno004'} folders

will fix and add a check to avoid this to be detected too late