Merge upstream/master
[Alt-Tab] Add _exiting flag. Activate windows in a standard way.
[Alt-Tab] Try to ensure that all the windows of the current desktop are in view initially.
[Alt-Tab] Small overview of exit logic.
[Alt-Tab] Slightly faster first preview.
[Alt-Tab] Stop experiment with slight color tint of active preview. Hard-code an almost opaque preview backdrop.
[Alt-Tab] Add a shortcut (CTRL+m) which in persistent mode moves the current window to next monitor.
[Alt-Tab] Add more persistent-mode shortcuts. Update labels and indicate minimized windows.
Ctrl+n: minimize
Ctrl+r: restore