CB-5290 iOS: Updated launch images sizes to include the status bar region

Launch images for all devices must include the status bar region.
For iPad portrait:
1536 x 2048 pixels
768 x 1024 pixels (standard resolution)

For iPad landscape:
2048 x 1536 pixels
1024 x 768 pixels (standard resolution)

https://developer.apple.com/library/ios/documentation/userexperience/con
ceptual/mobilehig/LaunchImages.html