Track provenance of derivatives

[tsalo]

Closes #548.

To do:

• Load metadata from the source BOLD file, and pass it along to derivatives.
• Filter metadata dictionaries based on the needs of the specific derivative.
  • For example, ALFF and ReHo maps shouldn't have the RepetitionTime field.
• Add extra fields as necessary.
  • For example, the SpatialReference field is required for fsLR data, AFAICT.
• Identify any files feeding into each derivative.
  • The obvious one is the BOLD file, but there are probably others (e.g., confounds files for denoised data).

Changes proposed in this pull request

• Update utils.bids.write_dataset_description to define a DatasetLinks field, if necessary, and add the preprocessed data path to it.

Documentation that should be reviewed

[tsalo]

Closing in favor of #966.