Fix/removes check json
The function was not working and the triggers prevent the deletion of ngrams. Merging this and updating db accordingly is necessary for the deletion feature I'm working on.
This commits also removes *.sql from .gitignore as it makes sense for me to version control those files.
Also I would like to open a discussion about the migration files name. I think it would be easier to name them like that <incremental_id>_what_this_file_does.sql instead of matching the name of the current gargantext backend id.