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

sky/examples/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;
-    opacity: .75;
-}
-
-log {
-    display: paragraph;
-    margin-top: 50px;
-}
-</style>
-<log>Touch the screen!</log>
-<script>
-import "dart:sky";
-
-// Material design colors. :p
-List<String> colors = [
-  "#009688",
-  "#FFC107",
-  "#9C27B0",
-  "#03A9F4",
-  "#673AB7",
-  "#CDDC39",
-];
-
-Element whichDot(event) {
-  return document.querySelector('dot[id="${event.pointer}"]');
-}
-
-void moreDots(event) {
-  Element dot = document.createElement('dot');
-  dot.setAttribute('id', "${event.pointer}");
-  dot.style['background-color'] = colors[event.pointer.remainder(colors.length)];
-  document.querySelector('sky').appendChild(dot);
-  runToTheCenter(event);
-}
-
-void goAway(event) {
-  whichDot(event).remove();
-}
-
-void stopDots(event) {
-  for (Element e in document.querySelectorAll('dot'))
-    e.remove();
-}
-
-void runToTheCenter(event) {
-  double radius = (5 + (95 * event.pressure));
-  Element dot = whichDot(event);
-  dot.style["transform"] = "translate(${event.x-radius}px,${event.y-radius}px)";
-  dot.style["width"] = "${2 * radius}px";
-  dot.style["height"] = "${2 * radius}px";
-  dot.style["border-radius"] = "${radius}px";
-}
-
-void main() {
-  document.addEventListener("pointerdown", moreDots);
-  document.addEventListener("pointermove", runToTheCenter);
-  document.addEventListener("pointerup", goAway);
-  document.addEventListener("pointercancel", stopDots);
-}
-</script>
-</sky>