Fix AppRegistryNotReady error for panels that load models.
Fix AppRegistryNotReady error for panels that load models.

The import to the debug_toolbar.middleware also loads all panels.
As a panel might be using Django models, such import happens too early.

jazzband/django-debug-toolbar,pevzi/django-debug-toolbar,pevzi/django-debug-toolbar,tim-schilling/django-debug-toolbar,spookylukey/django-debug-toolbar,tim-schilling/django-debug-toolbar,jazzband/django-debug-toolbar,spookylukey/django-debug-toolbar,tim-schilling/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar,barseghyanartur/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar,django-debug-toolbar/django-debug-toolbar,barseghyanartur/django-debug-toolbar,spookylukey/django-debug-toolbar,barseghyanartur/django-debug-toolbar,jazzband/django-debug-toolbar,pevzi/django-debug-toolbar