Change layout of splash dialog when orientation changed

Developer will provide two splash screen images for landscape and portrait mode.
Currently it will auto stretch the splash screen layout when orientation changed.
This fix can change the layout as developer needed for different orientations.

BUG=XWALK-1810
(Cherry picked from commit c1d4ce9a334d9592769f327ed5accc67d03ec53c)
Merge pull request #112 from kurli/splash_screen_layout

Change layout of splash dialog when orientation changed