[server] move security/integrity hook management away from InternalSession.__init__ and to Repository.internal_{session,cnx} instead. Lets internal_cnx avoid deprecation warnings.

../../doc/book usr/share/doc/cubicweb-documentation
../../doc/html usr/share/doc/cubicweb-documentation
../../debian/cubicweb-doc usr/share/doc-base/cubicweb-doc