[CONV] ADNI-TO-BIDS/IXI-TO-BIDS : Standardization of the -sl option to -tsv

[AliceJoubert]

In an effort to harmonize the options of the command lines available in clinica, the option --subjects-lists (-sl) for the converter adni-to-bids should be progressively replaced by the option -tsv which is commonly used in pipelines. The modifications should :

• add -tsv option for converters
• detect format (.txt or .tsv) :
  • if .txt : indicate coming-up deprecation of the -sl option and ask the user to change format + add column name ; still take that format for now
  • if .tsv : take the format
• add unit test if not present
• indicate change in docs + give example with right format
• should be done for both ADNI and IXI converters