allow to directly query the content of tsv files

[Remi-Gau]

one thing I can think of: similar to querying file paths of tsv files with a particular suffix:

bids.query(BIDS,'data','extension','.tsv','suffix',{'channels','events'})

the user could request the contents of particular tsv types (scans.tsv or sessions.tsv, but also channels.tsv, events.tsv, or whatever the case may be)

Originally posted by @coxroy in #542 (comment)

[Remi-Gau]

closed by #555