CB-2527: Update iPad splash images to correct sizes

-Updated the following images to avoid shifting down of splash during startup:
 Default-Landscape~ipad.png   (1024x748 pixels)
 Default-Portrait~ipad.png    (768x1004 pixels)
-Reference document:
 http://developer.apple.com/library/ios/#documentation/UserExperience/Conceptual/MobileHIG/IconsImages/IconsImages.html