[Android] Support immersive fullscreen mode for LaunchScreen

For Android version >=KikKat, fullscreen mode should be immersive fullscreen mode.

BUG=XWALK-1593
When set fullscreen to true in manifest, the theme.xml will set android:windowFullscreen to true, same as WindowManger.LayoutParams.FLAG_FULLSCREN.
Refer to http://developer.android.com/reference/android/R.attr.html#windowFullscreen
I have also tested on Android 4.4.4, the flag is also true in fullscreen mode, So I think it's workable on all versions.