Django-graphql-jwt

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* Fixed context.META attribute

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* Removed environment settings variables
* Added JWT_AUTH_HEADER setting
* Added JWT_PAYLOAD_GET_USERNAME_HANDLER setting
* Fixed TokenAuth mutation when user is already authenticated

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* Added JWTSettings
* Added jwt-handlers to settings
* Added context argument to jwt-handlers

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* Included auth decorators

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* Added old style middleware support

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* Added anonymous-hyperlink