Drone Swarm 0.6

Another quick update on this project:

• colored area around stations again
• levels with more than one AI to fight
• swapped level 2 and 3 (thanks to orochii)
• 3 more levels
• saved level progression on user home dir on disk

Not too much crazy, but another little step on right direction! Let me know if you find any bug or you have any suggestions, much appreciated!