Include django contrib in stack 505

The list for ```HIDE_IN_STACKTRACE``` is rather long now and it has to be manually edited if modules are added/removed to Django. We could potentially programmatically loop through the modules of ```django```.
Ups, I found it tries to import these modules. But looking at code of [omit_path](https://github.com/django-debug-toolbar/django-debug-toolbar/blob/master/debug_toolbar/utils.py#L46), it is sufficient to have only `django` module in `HIDE_IN_STACKTRACES` to ignore all submodules too. Why do you decided to add submodules there?