Optimizations and small feature

Changes to the browser version

• Removed the light source and shadows cast by the light source of the torches (Should make the browser version a lot more friendly and lighter to run)
• Made the cave background darker
• Added a 'close' button for the 'input user name' window when you die

Changes to the downloadable client version

• Made the cave background darker 
• Added a 'close' button for the 'input user name' window when you die