Added braces to if-statements (jslint-error) and updated TODO-list
Created a Start-game-message which disappears when pressing a key

Added some temporary css and a div in the html-file. Prepared for a Game over situtation by creating
a startGame()-function, instead of depending on reloading the browser.
Removed out commented code
Removed initialization of some "global" variables and initializes them when the game starts instead
Added game over function, which displays a game over message to the user

Is temporarily triggered by pressing "x" on the keyboard for debugging purposes.