Ridi-django-oauth2-resource

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- Test travis deploy

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- Remove `expire_margin`

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- Change primary field type in RidiUser
- Implement __str__ in RidiUser

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- Rewrite code structure in ridi_oauth2 package.
- Change grant object, change logic for check scope and ...etc
- Add migrations about RidiUser Model
- Configure travis

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Fix
- Fix login_required Decorator

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Register New Package
- Addition of initial functions related to OAuth2.
- Pure Python Client
- Django Binding
- Django Binding Library reflected the policy of RIDI.