Added History Mode and Arcade Mode

• Added 2 modes to play instead the one which was before:
  • History: Where we can pass levels and get throught the plot of the game.
  • Arcade: Where we can choose levels and play them to get credits

• Change the art of the game, now almost all the images are new
• Now, when we finish a level we get the credits of the level, to buy new powerUps.

Fixed bugs when we upgrade features of the ships