Make `SLPickerViewTest` 64-bit compatible.
`-[UIView slAccessibilityIsVisible]` now reports an element's visibility on-screen,
regardless of window. (fixes #212)

That is, `-slAccessibilityIsVisible` will now properly report the visibility of views
in any window, even non-key windows; and `-slAccessibilityIsVisible` will now
properly report whether a view is visible on-screen, not merely within its window
(i.e. it will report `NO` if a view is occluded by the contents of a window above its window).

This removes the need for `SLPickerView` to use `UIAElement.isVisible`
(in order to match pickers used as input views).
Allow SLAssert methods to be called from non SLTest subclass methods
Merge pull request #215 from inkling/jeff/multiwindow_visibility

`-[UIView slAccessibilityIsVisible]` reports an element's visibility on-screen, regardless of window.
Incorporate PR feedback

Adding a comment to SLTest.h describing when SLAssert should be used
Renaming the static variables to use double underscores
Support for using a prebuilt app instead of building one (fixes #207)

This allows for decoupling of build CI and automation CI into two separate actions.
Merge pull request #217 from justinseanmartin/jmartin/allow-asserts-from-non-sltest-subclasses

Allow SLAssert methods to be called from non SLTest subclass methods
Merge pull request #218 from justinseanmartin/jmartin/allow-separated-build-from-testing

Add support for using a prebuilt app to allow decoupling of the tasks
Merge remote-tracking branch 'public/master' into add-exception-info

* public/master:
  Support for using a prebuilt app instead of building one (fixes #207)
  Incorporate PR feedback
  Allow SLAssert methods to be called from non SLTest subclass methods
  `-[UIView slAccessibilityIsVisible]` now reports an element's visibility on-screen, regardless of window. (fixes #212)
  Make `SLPickerViewTest` 64-bit compatible.

Conflicts:
	Sources/Classes/SLTest.m