Adopt to bug 1147, commit 2c88b6dfd4eb7e2cd9a50fa48e08ecafc980931a. Using the native unique deviceID makes monitor identification more robust.
7438540ee6604cf91e14f12da891834d4cd83cfe Changed as described .. This also allows us simplify displayID -> NSScreen-idx -> MonitorDevice into displayID -> MonitorDevice and to survive a primary monitor change.