Implement a better lighting system

This MR completely refactors how lighting works in the game and implements the required systems to allow that. This includes a new set of shaders to better store different lights and allow multiple at a time. A new set of structs to easily store lighting data in the game, and a LightManager class which stores these structs to easily share them between objects. This new lighting system has currently only been applied to the Cube object, and a separate MR will implement it for Textured objects.