Clinica 0.4.1 - Deeplearning-prepare-data (for pet-linear output), converters updates and some minor fixes

Added

• [deeplearning-prepare-data]: Add option to run pipeline with pet-linear outputs

Changed

• [Oasis-to-bids]: Remove FSL library dependency for OASIS-to-bids conversion.
• [Clinica]: Replace exception by warning when CAPs folder not recognized.
• [AIBL-to-bids]: Center output nifti files of AIBL.
• [AIBL-to-bids]: Extracts DICOM metadata in JSON files.
• [ADNI-to-bids]: Update image selection to always consider non-processed (original) images
• [merge-tsv]: Fetch sub-cortical volumes generated by t1-freesurfer pipelines and JSON
  files (if exists).

Fixed

• [pet-surface]: Verify SPM12 installation when running pipeline
• [docs]: Update instruction to install some third party software