Update: scoreboard and flair

What's new:

• Basic scoreboard: counts kills (when the other player dies because of a sawblade you've installed), deaths and picked up diamonds.
• Better player explosions (particles are matched to player colors, collide with walls and leave marks)
• Bugfix: you couldn't place sawblades where diamonds used to be. You can now.
• Temporary hotkey: you can toggle full screen mode with Shift+F.