Stop using class function `Application.all()`

[tmandry]

Writing protocols and fakes that emulate AXSwift.Application is annoying, because .all() has to be reimplemented for every class in the hierarchy. We should pass in something that emulates NSWorkspace rather than depending on Application.all().

I'm not certain whether this will reduce boilerplate or not. Even if it's about the same level of complexity, it's probably a win because it makes internal patterns more consistent.

[tmandry]

This got cleaned up in a recent-ish commit