Improve TransportController demo.

This is an actually realistic implementation of a
video player.  It's still delibrately simple, but it's
not outright broken.  We now have our own media controller
since that is the only way to get something that actually
works, we use system UI flags to hide nav/status bar when
playing, we use the new TransportController APIs to go
into a formal playback state where we take audio focus.

Change-Id: I19ac171483637b8ee94c9c07aea39c11748cbc46

samples/ApiDemos/src/com/example/android/apis/view/VideoPlayerActivity.java

@@ -167,7 +167,7 @@ public class VideoPlayerActivity extends Activity
                     h.removeCallbacks(mNavHider);
                     if (!mMenusOpen && !mPaused) {
                         // If the menus are open or play is paused, we will not auto-hide.
-                        h.postDelayed(mNavHider, 1500);
+                        h.postDelayed(mNavHider, 3000);
                     }
                 }
             }