netcontrol/core: Remove rules

For now, my priority is to have a stable code that only does one job: sit
between other devices and the router. This commit is a step back from what
I'd done at the beginning of the project. Rules will be implemented once
I have unit tests and a properly designed API. Until then, it's better to
avoid complexity and code that is not being used.
core/control.py: Rewrite import statement with absolute path

As with previous commits, imports must be used from the root `netcontrol`.