Fixed bug in publisher_publish management command

Added .distinct() on pages query (Page.objects.drafts().filter(title_set__published=True)), because .filter(title_set__published=True) can make duplicated page objects. This happens with multiple languages on one page - title_set__published causes Django to make a join, which in turn returns duplicated Page objects for a query. For this problem, pages with multiple languages were published multiple times (for each language).