Rename some Python scripts to be more explicit

[maximemulder]

When I arrived in LORIS, one of the challenges of getting to know the codebase what to learn what scripts to use for what purpose. I think the naming could be improved to make it more simple or explicit:

• run_dicom_archive_loader.py -> convert_dicom_archive_to_bids.py (the renaming I am the most interested in)
• run_dicom_archive_validation.py-> validate_dicom_archive.py (for consistency)
• run_nifti_insertion.py -> register_nifti.py (I like "register" to say we add something to the database without further processing it)
• run_push_imaging_files_to_s3_pipeline.py -> push_imaging_files_to_s3.py (never used this script though)
• bids_import.py -> import_bids.py (for consistency).

[maximemulder]

LORIS imaging meeting: The 27 release is already packed with changes, so this will probably be done in the next release.