Move sky/examples to sky/sdk/lib/example, and code changes to support that change. Fixes T277.

sky/sdk/lib/example/raw/touch-demo.sky

 #!mojo mojo:sky_viewer
 <sky>
 <import src="/packages/sky/framework/debug/shake-to-reload.sky" />
 <style>
 dot {
     position: absolute;
     height: 10px;
     width: 10px;
     background-color: #00FF00;
     border-radius: 5px;
@@ skipping 50 matching lines @@
 }
 
 void main() {
   document.addEventListener("pointerdown", moreDots);
   document.addEventListener("pointermove", runToTheCenter);
   document.addEventListener("pointerup", goAway);
   document.addEventListener("pointercancel", stopDots);
 }
 </script>
 </sky>