Fixes for endless mode

Here with some fixes!

• When getting more invincibility frames, the animation now shows that.
• Getting a speed up now properly speeds up your animation.
• Changed the STUFFIER upgrade visual change to be easier on the eyes.

And some balancing shenanigans!

• Updated with kinder leveling on enemy spawns on endless mode
• Made the boss in endless mode scale correctly
• Changed some endless mode layouts to give the player a bit more space