Layout and PiP improvements, new settings

- player is now a separate window on macOS
- add setting to disable pause when player is closed (fixes #40)
- add PiP settings:
  * Close PiP when starting playing other video
  * Close PiP when player is opened
  * Close PiP and open player when application
    enters foreground (iOS/tvOS) (fixes #37)
- new player placeholder when in PiP, context menu with exit option

Shared/Views/VideoContextMenuView.swift

@@ -64,7 +64,7 @@ struct VideoContextMenuView: View {
             if inNavigationView {
                 playerNavigationLinkActive = true
             } else {
-                player.presentPlayer()
+                player.show()
             }
         } label: {
             Label("Play Now", systemImage: "play")