Add an AssetManager class that manages assets #5
Description
Create an assetmanager class that loads up required assets and does not repeat any loads.
For example, sprites can be stored in a sprite class, of which assetmanager keeps track of all sprites loaded for the game/scene, and lets the appropriate sprite renderer use the appropriate sprite, instead of loading multiple instances of the same sprite into memory.
Especially helpful when developing a game that for example uses a texture for bullets/particles. Instead of loading 100x the memory for the texture of a bullet, it just loads one.