Add support for UIPickerViews in Subliminal

UIPickerViews are under a different Window other than keyWindow, so I had to find the other one.  Otherwise it is pretty straightforward.  I'm leaning on the UIA methods a bit more heavily for interacting with the element, but open to suggestions.

Added one fairly comprehensive test case.
Ok, pulled those out for all the SLPickerView comments. Thought it would be nice to understand for someone who knew it from a UIA perspective, but I get the concern. It should be irrelevant (and pretty obvious) as to how it is implemented.