add test config for django 1.7
add django.setup() in test runner for django1.7
Update test settings and utils for Django1.7

 - Set package name explicitly on INSTALLED_APPS. Fixes "Item" import
   issue.
 - Add MIDDLEWARE_CLASSES to suppress warning.
 - Add "enter" keyword to util sending ``setting_changed`` signal:
   https://docs.djangoproject.com/en/dev/releases/1.7/#signals
 - Change ``mimetype`` to ``content_type``
   https://docs.djangoproject.com/en/dev/releases/1.7/#features-removed-in-1-7
Merge pull request #318 from yourcelf/dj1.7

Update test settings and utils for Django1.7
Fix installed apps in tests for Django < 1.6
Update readme with info about django 1.7 support
Merge pull request #308 from mariocesar/dj1.7

Support for django 1.7