Snap.html: Focus the world canvas on startup

so Snap reacts to keyboard events right away (without having to click
on the IDE first)

history.txt

@@ -2128,4 +2128,5 @@ ______
 
 140520
 ------
-* Morphic: Prevent default action for ctrl-/cmd-key events
+* Morphic: Prevent default action for ctrl-/cmd-key event
+* Snap.html: Focus the world canvas on startup, so Snap reacts to keyboard events right away

snap.html

@@ -22,6 +22,7 @@
 			var world;
 			window.onload = function () {
 				world = new WorldMorph(document.getElementById('world'));
+                world.worldCanvas.focus();
 				new IDE_Morph().openIn(world);
 				setInterval(loop, 1);
 			};