Balancing and Polish

I replaced the old default buttons for the victory and game over screens with this new planet art I made.

I also rebalanced the game to make it a little easier. Enemies and their lasers now move slower to prevent the most annoying type of loss where you fly into something you couldn't see off screen.  Enemy lasers will also no longer get faster as the difficulty ramps up so you can more easily dodge them later in the game. This update doesn't just make the game easier however. Enemies will now spawn at slightly faster rates, especially at the highest difficulty.

This update should help bring down the difficulty, especially for lower difficulty settings, while keeping things interesting with larger waves of enemies.