Djedefre

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* Refactor urls to use new RESTful ViewSets
* Retain old urls for compatibility
* Add Django 2.0 to tox.ini
* Add DRF 3.8 to tox.ini
* Drop Django 1.10 support
* Update requirements.txt
* Update travis.yml
* Update .gitignore

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* Add Steam config to testproject
* Add python egg data to .gitignore
* Update social auth serializer to use GET parameters instead of JSON data
* Update python-social-auth integration tests to use GET parameters
* Update social auth credentials in testproject to use environment variables by default

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* Add proper validation errors for OAuth state validation

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* Update python-social-auth load strategy invoke to use proper requests

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* Fix: Request data is not available in python-social-auth backends

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* Fix: Token Strategy breaks in all cases if djangorestframework-jwt not installed

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