* geis does not work with channels2 and never will be (it has to be python now)
* pytest
* rewrote cache system
* use username instead of pk for admin user in tests
Uses django channels instead of tornado for the autoupdate. Therefore
tornado is nolonger a dependency of OpenSlides (but channels).
This uses websockets instead of SockJS.
Use the flag insecure in the start command to provide static files serving.
Use a new session backend that has a ForeignKey to User.
Refactored user creation and update via REST API. Used new serializer.
Cleaned up management commands, signals and imports. Moved code from 'api.py' to 'models.py'.
Changed usage of group 'Registered'. Now the users don't have to be members to gain its permissions. Used customized auth backend for this.
Added and changed some tests.
