feat: add a collection of levels to slowly ramp-up the difficulty

[CallumDennisIE]

Added three levels to the game. To slowly ramp up the difficulty to the player and teach them the mechanics. This could be used as a tutorial of sorts

• The first level is a static stormtrooper - Teaching the player how to shoot.
• The second level is static stormtroopers behind cover, teaching the player that they will have to aim to be effective.
• The third level is where some stormtrooper will dodge out of the way of shots and also use cover.

[CallumDennisIE]

I'm actually going to close this, as on looking back they are a bit rubbish. Will try again.