Optimizations Part 5: New Sprite Loading System for 20 min Exercises

* New more effective sprite loading system added for 20 min exercises at all levels. Fantastic news that the sprites / exercises are loading a lot smoother now from player feedback. This motivates me as I know that these optimizations are actually working. I will now get cracking re-coding the 30 min exercises onto the new sprite loading system and will release another patch update soon.