Deprecate participant_label and exclude_participant_label args

[pvandyken]

Once we finish implementing the filtering apis #241, the participant_label and exclude_participant_label arguments on generate_inputs() become rather redundant. There would, at that point, be three separate ways to filter out subjects: BidsDatasets.filter(), the magic --filter-<component> args, and the generate_inputs() arguments. I think we can probably afford to simplify and deprecate.

[akhanf]

If this would also deprecate the --participant_label cli arg, then that would be a deviation from bids-app standards, and it is a quite commonly used option in my experience. We could drop the exclude_participant_label perhaps.

[pvandyken]

Ah, no definitely not talking about the cli. I was thinking more the arguments on the generate_inputs function

[tkkuehn]

The CLI arg uses this so we should keep it for now, at least until BidsDataset.filter exists.

[pvandyken]

As implemented in #344, these arguments actually do have distinct features: they apply filtering after paths are found via pybids, meaning you can end up with empty components as opposed to missing components. --participant-label also filters before running path parsing, meaning it's faster than running a filter after generate_inputs