[dbapi] move ProgrammingError into cubicweb module
A new ``repoapi`` will be introduced as a replacement for the dbapi. It will
need ProgrammingError too.
Related to #2503918
# -*- coding: utf-8 -*-
# copyright %(year)s %(author)s, all rights reserved.
# contact %(author-web-site)s -- mailto:%(author-email)s
#
%(long-license)s
"""%(distname)s entity's classes"""