Move nnwindowstore to a service
WIP: Window group coalescing appears to be working correctly. UI disabled, services partially done.
Selector object and tests, plus regression tests ported over for window list service (spoiler: they fail)
Window grouping tests all pass!

Now to get this app working again.
Next up: window views and wiring AX back in
Re-enable preferences, status bar item, simplify view vending, fix tests.
Window snapshots are complete again, thumbnail view is fully stubbed out.
Breadcrumbs and removal of content updates from core window controller.
It's not perfect (for some unknown reason), but thumbnails draw now.
Edge case to fix with Tweetbot-specific quirks

Or any application that's bad at naming windows, really. I wonder if I
should distinguish between empty string and no name at all?
Copy edit.
Match interface to match the currently-shipped Switch for now

Something weird with subwindows and I really want to get an update out
that fixes the first launch experience.
Well that's now been tested.
AX scaffolding and some cleanup.
Switch functions again! Time for testing and a few minor improvements to avoid regressing performance too much.