[iOS / String UI Picker] - Fixed bug 23161, iOS 8

- Fixed bug 23161, since UIActionSheet is deprecated in iOS 8 and the
new UIAlertController doesn’t support subviews, I had to create a
complete new animated view for the StringUIPicker.
- I also took that opportunity to update the new view to iOS 7 & 8
translucent effect instead of a basic alpha transparent effect.