Drf-jwt-devices

Fixed
- fixed exception check in views

Added
- a test to enforce completeness of migrations
- missing migration

Added
- few minor utilities to make the project be easier to extend
Fixed
- passing custom serializer context to devices refresh view
Removed
- support for Python 2.7

Added
- Device list in Django admin

Added
- Device model
- DeviceViewSet
- ObtainJSONWebToken view
- DeviceRefreshJSONWebToken view
- DeviceLogout view
- PermittedHeadersMiddleware