Day 20: Light Refactoring, part 1

Today i refactored all the light classes in C++, and added parameters like specular color or specular intensity, which i'll use in the future.
Now each light inherits from a AbstractLight class.

The engine does exactly what it did yesterday, but now the lights are way easier to manage.

Tomorrow i'll refactor the light calculations in the shaders, and soon I'll add specular lightning.

I also plan to add spot lights, which is not the most exciting thing, but needs to be done.