Native migrations v/s South migrations from Django 1.7 onwards

[scdoshi]

Figure out if possible to support both. Will also affect post_syncdb/post_migrate management functions.

[sherzberg]

@scdoshi I've started to port to django 1.7. I will try to get it in a good state to send a pull request.

https://github.com/sherzberg/django-notifier/tree/1.7-support