Add support for the SupportedUserInterfaceIdioms attribute.

As the documentation says:

Key | Value type | Value
--- | --- | ---
SupportedUserInterfaceIdioms  | Array | Indicates that the element is displayed only on specific types of devices. The value of this key is an array of strings with the supported idioms. Include the string “Phone” to display the element on iPhone and iPod touch. Include the string to “Pad” to display it on iPad. This key is available in iOS 4.2 and later.