The MCFLIRT descriptor doesn't have a proper custom section for special Boutiques modules

[prioux]

It's set as:

  "custom": {
    "BoutiquesOutputFileTypeSetter": {
      "out_file_outfile": "NiftiFile",
      "out_grefvol_file": "NiftiFile",
      "out_meanreg_file": "NiftiFile",
      "out_meanvol_file": "NiftiFile",
      "out_sigma_file": "NiftiFile",
      "out_variance_file": "NiftiFile",
      "out_mats_directory": "FileCollection",
      "out_par_file": "TextFile"
    }
  }

[natacha-beck]

Close by #272