Graphene-django-extras

1. Added **queryset** options to **DjangoListObjectType** Meta class for specify wanted model queryset.
2. Added **AuthenticatedGraphQLView** on **graphene_django_extras.views** for use ‘permission’, ‘authorization’ and ‘throttle’ classes based on the **DRF** settings. Special thanks to **[jacobh](https://github.com/jacobh)** for this [comment](https://github.com/graphql-python/graphene/issues/249#issuecomment-300068390).

1. Fixed bug on subscriptions when not specified any field in "data" parameter to bean return on notification message.

1. Fixed bug when subscribing to a given action (create, update or delete).

2. Mini web tool to test notifications of graphene-django-extras subscription. It is intuitive and simple:
[graphene-django-extras subscriptions tool.zip](https://github.com/eamigo86/graphene-django-extras/files/1411020/graphene-django-extras.subscriptions.tool.zip)

1. Added support to multiselect choices values for models.CharField with choices attribute, on queries and mutations. Example: Integration with **django-multiselectfield** package.
2. Added support to **GenericForeignKey** and **GenericRelation** fields, on queries and mutations.
3. Added first approach to support **Subscriptions** with **Channels**, with subscribe and unsubscribe operations. Using **channels-api** package. :trophy:
4. Fixed minors bugs.

Changed dependency of DRF to 3.6.4 on setup.py file, to avoid an import error produced by some changes in new version of DRF=3.7.0 and because DRF 3.7.0 dropped support to Django versions < 1.10.

1- Fixed bug on **DjangoInputObjectType** class that refer to unused interface attribute.
2- Added support to create nested objects like in **DRF** (http://www.django-rest-framework.org/api-guide/serializers/#writable-nested-representations), it's valid to **SerializerMutation** and **DjangoInputObjectType**, only is necessary to specify _nested_fields=True_ on its Meta class definition.

3- Added support to show, only in mutations types to create objects and with _debug=True_ on settings, inputs autocomplete ordered by required fields first.

4- Fixed others minors bugs