Adding Swagger setting for using one or more parsing classes for the base api view.

Swagger fails to parse API pages that use more than JSON renderer.

Was hitting an issue where the swagger javascript failed to parse the JSON, This was due to the page was not json it was the API view from the django rest framework.

new optional setting:
SWAGGER_SETTINGS = {
    "exclude_namespaces": [],
    "api_version": '0.1',
    "api_path": "/api",
    "enabled_methods": [
        'get',
        'post',
        'put',
        'patch',
    ],
    "api_key": '',
    "is_authenticated": False,
    "is_superuser": False,
    "renderer_classes": ('rest_framework.renderers.JSONRenderer',),
}