[dataimport] massive renaming of session to cnx
and make NoHookObjectStore working with the new connection handling.
Closes #4891547
option_group_changed('port', 'main', 'web')
option_group_changed('query-log-file', 'main', 'web')
option_group_changed('profile', 'main', 'web')
option_group_changed('max-post-length', 'main', 'web')