* Add ability to pass `execution_context_class` to `GraphQLView.as_view()`
Currently when passing `execution_context_class` like this:
```
GraphQLView.as_view(execution_context_class=CustomContext)
```
you get the following error from `View.as_view()`
```
TypeError: GraphQLView() received an invalid keyword 'execution_context_class'. as_view only accepts arguments that are already attributes of the class.
```
this PR fixes the `hasattr` check in `.as_view`.
Fixes: #1072
* make black happy
removed whitespace
* merge master into v3
* fix order_by snake casing by checking if value is None, switch executor to execution_context_class since schema.execute no longer supports executor
* fix linting by removing duplicate defintion and test of convert_form_field_to_string_list
* Add integrity checks for GraphiQL CDN resources
Also fixes an erroneous assignment preventing a setting from getting to
the UI.
* Pass SRIs and new versions to the template
* Update hashes
* Use SRI-stable artifacts for GraphiQL resources
* Remove Python 2 support
* Upgrade Python & Django versions
* Remove unsupported Django versions
* Remove unsupported Python versions
* Add Python 3.8
* Drop support for django-filter < 2
* Update LoginRequiredMixin doc link
* Remove redundant import
* Resolve RemovedInDjango40Warning warnings
* gql/graphene-django/graphene_django/tests/test_converter.py:175:
RemovedInDjango40Warning: django.utils.translation.ugettext_lazy() is
deprecated in favor of django.utils.translation.gettext_lazy().
* graphene-django/graphene_django/utils/utils.py:28:
RemovedInDjango40Warning: force_text() is deprecated in favor of
force_str().
* No need to use unicode strings with Python3
* Remove singledispatch dependency
singledispatch is inluded with Python >= 3.4, no need for external
package.
Graphiql has a history tool that allows you to save and label favourites, but this version has a bug (fixed https://github.com/graphql/graphiql/issues/750). This change upgrades to the latest version.
operationName is serialized into the query string as a string. When getting the query value for operationName, we need to convert string "null" into None.
