V0.2: Keys and Treasure Chests

Small changes and bug fixes:

• Keys and Chests added. Now opening the chest/s is required to win the level instead of picking up the items.
• More detailed Game Over messages
• Simplified in-game UI
  
• Screen size adapts to vertical and horizontal orientations
• Tank air does not go down when swimming near the surface
• Bug fixed for not being able to finish level 2
• New Level: 3