Default path_pattern for build_path?

[kinleyid]

It seems like BIDS already defines the path_pattern argument to bids.layout.writing.build_path. Perhaps this should be the default? Or a get_default_path_pattern(modality) function could be defined to get defaults for different modalities?

[effigies]

This would need to be done from the schema. @astewartau has started on building a configuration from the schema in #1163. Building the path patterns from the file rules would be a definite improvement over the current method of updating them manually.