Smart pointers and const correctness

[vexyl]

Refactor code to use smart pointers and to be const-correct. I've already ran into a lot of issues using raw pointers. Const-correct code is less error prone and looks cleaner.

[GiantCrocodile]

What was your issue with raw pointers? I agree that we should have const everywhere where it fits. For example every getter and functions which just print stuff to console or file should be obviously const.