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

iOS/Info.plist

@@ -15,6 +15,11 @@
 			</array>
 		</dict>
 	</array>
+	<key>UIApplicationSceneManifest</key>
+	<dict>
+		<key>UIApplicationSupportsMultipleScenes</key>
+		<false/>
+	</dict>
 	<key>UIBackgroundModes</key>
 	<array>
 		<string>audio</string>