xASL_init_CreateParticipantsTSV does not check rawdata

[HenkMutsaerts]

Description

xASL_init_CreateParticipantsTSV does not check rawdata, only the studyroot and derivatives folders.
Just checking @jan-petr if I didn't fix this already in our revamp, otherwise I will fix this now.

Tasks

• Wait till Master issue revamped subtraction #1551 and PWI4D & session concatenation follow-up #1543 are merged to develop before creating this branch
• Create capital-insensitive list of datasetRoot, rawdata, derivatives participants.tsv
• By priority go 1) derivatives (if already existed), 2) rawdata (per BIDS), 3) datasetRoot
• Generate warnings if it was provided at the wrong location
• Generate warnings if multiple participants.tsv existed

Deal with participants.tsv conversion from BIDS sub- to legacy sub-_1

• Add sub- if missing
• Add ses- if missing in session_id column
• from participant_id and session_id columns, generate legacy subject-name including visit

Merging

• Do we want to merge in case of different participants.tsv?
• xASL_bids_Add2ParticipantsTSV already has some functionality for this, can we reuse this?

PM (pro memoria)

• We might want to change x.S.SetsID -> x.S.participantsTSV or something, to harmonize those

How to test

Optional: insert description about how to test the code changes here

Release notes

Required: summarize the changes for the release notes here