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.
Yea, I was going on the verbose side, but I didn't really split what should be in the appledoc versus what should be in the implementation comments. I'll scrub this.