[Android] Add the method of onWindowFocusChanged() in app template.

In Android 4.4 immersive sticky full screen mode, the specific method of
onWindowFocusChanged() needs to be handled in the application activity.
For the generated application based on Crosswalk application template,
if the method is not added, the operation of swiping up from the screen
bottom is failed. This fix adds this method in application template.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1200