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.
This should probably be split out into smaller test cases. When all the assertions together are in one method, its easier for the individual assertions to interfere with one another (e.g. an earlier test case might do something innocuous that breaks a later test case).

Additionally, because the test case names are used to report the test results, you end up with better, more accurate output as to what tests failed and passed. Finally, splitting up into separate methods lets you run an individual one using `focus_`, which would be nice if you were debugging just that one.