Improve mousemove/mouseup when dragging outside the game canvas

[jefvel]

Currently, if a player clicks and drags the mouse outside the game window, it'll act as if the mouse was released. It's not consistent with the other non-HTML5 targets.

This PR fixes that. It makes it possible to click, drag, and move the mouse outside the game window. If the user releases the mouse button outside the window it'll trigger as expected.

I've tested this in chrome+firefox and iOS and Android.

An optional feature would be to add the following CSS to the index.html file.

      html,
      body,
      canvas {
        touch-action: none;
        touch-action-delay: none;
        user-select: none;
        -webkit-tap-highlight-color: transparent;
        -webkit-touch-callout: none !important;
        -webkit-user-select: none;
        -moz-user-select: none;
        -ms-user-select: none;
      }

However, it's not really needed. But it helps on mobile targets.

[RowanFuture]

+1 this would be great