Fix positioning in iOS 8

[alexwald]

• Transforms are no longer applied to windows for rotation, so ignore orientation specific logic
• Use window instead of screen for bounds (screen returns rotated bounds on iOS 8)

[alexanderjarvis]

Hi, do you think this might be a better way of solving the problem?

https://github.com/bryanwayb/PXAlertView/commit/0a9d475fb5b5f38a852af06f2b0c1d0b3a2db8a1