[schema] Use TZDatetime for creation_date and modification_date No work has been done for form fields/widgets since creation_date / modification_date are by default not editable through the default UI. One may want to add such feature at some point. Time will be displayed as UTC, let the end-application decide otherwise by customizing the tzdatetime printer if desired. Closes #4848923

usr/lib/python2*/*-packages/cubicweb/entities/
usr/lib/python2*/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/python2*/*-packages/cubicweb/*.py