Add fading out ability to all entities.
Add a way to render an overlay while switching a screen.
Should later be used when losing a game and then switching to the
highscore screen.
Added a way to fade in or out anything.
I seem to be on a fading trip today. Save yourself whilst you can.
Implement Fading in Entity.
Added a temporary version of the TimeAttackAsteroidSpawner.
Currently does not increase difficulty over time and is thus also not
balanced at all.
Let's just use a unity matrix. Cleaner, less messy position setting.
Let MenuScreen fade out and then start the game properly.
Make StoneAsteroids invulnerable to damage directly after splitting.