* Every file work with it own, 1th level child only, to prevent massive logic levels keeping in mind
* To access any children features, deeper or higher than 1th level of current class, use delegation methods (actions, getters and setters)
* One file - one class. If the file requires additional (GTK) component, this component should be placed at similar folder with same name as parent filename. So we have simple hierarchy navigation logic - from app to window, from window to it container, etc.
* At this moment, all constants named with uppercase, const everything that not mutable