Come up with a better segregation by modules compared to currently existing `base.py`, `core.py` and `models.py`

[Oleksandr Tereshchenko]

The current problem is that segregation by base.py, core.py and models.py is somewhat arbitrary and mostly revolves around dodging the circular import problem instead of the pursuit of meaningful separation of code. This is happening because the names of the modules are way too generic.