Create a single package Cryton with optional installs

We could switch to extras since it's complicated to version and install Cryton with its many components.

pip install cryton[core]

User wants to deploy Cryton and he has to make sure that the versions match for each component.

Easier and more unified version management and installation.

Django uses this feature I think.

The extras could be listener, scheduler, worker, and cli. Or more defining core , worker, and cli.