Release/0.4/backport/unicodecsvwriter

Backport 7355d5a22468d6aaaf120c98cd988d42453d76a8 to 0.4 to be used by labour-campaigncreator, as downloading an orders report as csv from the dashboard displays the header row as `<django.utils.functional.__proxy__ object at 0xb0bb55ec>`, because of ugettext_lazy.