Prevent default browser action for SPACEBAR and ARROW keys

SPACEBAR scrolls the page down on some browsers, and ARROW keys
may also cause the page to scroll. Now the game prevents the
browser from performing these default actions when the game is
in focus.

Also, I removed an unused optional parameter from putText,
because Internet Explorer was complaining about it. The game
still doesn't work with IE though, because SVGs are not displayed.

	modified:   shapeshift.js