jsonalchemy: add `jsonext` as common namespace
jsonalchemy: add `jsonext` as common namespace

Signed-off-by: Esteban J. G. Gabancho <03cb568148df368b792a31d9c4d06b12dc802700@gmail.com>

inveniosoftware/invenio,inveniosoftware/invenio,tiborsimko/invenio,tiborsimko/invenio