django.utils.simplejson removed in 1.7

* django_newsletter/utils/ofc.py: Import dumps from base json library
Updating get_query_set to get_queryset, etc

* django_newsletter/admin/contact.py (ContactAdmin.filtered_request_queryset): Edit
* django_newsletter/admin/newsletter.py (BaseNewsletterAdmin.get_queryset): Edit
All forms need either fields or exclude property

* django_newsletter/admin/smtpserver.py (SMTPServerAdminForm.Meta): Add
  all fields
Two more url templatetags typos

* django_newsletter/templates/newsletter/newsletter_historic.html
* django_newsletter/templates/newsletter/newsletter_statistics.html
Update migrations from South to built-in Django
Move get_newsletter_storage_path to top-level

* django_newsletter/models.py: Moved out of the Attachment class.