Added gun, fixed bugs

I fixed some bugs:

• Player stays on planet, instead of gradually moving further away
• Furniture doesn't blend into the background-colour (of a house)
• The player can now blink
• Started with the layout for in-game quests and messages
• And a lot of tiny details

I also added the basic gun mechanism:

• Clicking anywhere shoots bullets in that direction. (With a certain delay.)
• If a bullet hits an asteroid, the asteroid explodes.