[dataimport] simplify SQLGenSourceWrapper.add_info
At this point 'CWSource' is a thing (we're not in the middle of a
migration), and source.eid won't be None (we read it from the db)
ensure .tox is blacklisted when recursing on the fs to get some files
among others, avoid crash when using 'c-c i18ncube' on a cube using tox.
Closes #10429317