[iOS] Mark the app as VoIP

ios/app/Info.plist

 		<string>jitsi.ttf</string>
 		<string>FontAwesome.ttf</string>
 	</array>
+	<key>UIBackgroundModes</key>
+	<array>
+		<string>audio</string>
+		<string>fetch</string>
+		<string>voip</string>
+	</array>
 	<key>UILaunchStoryboardName</key>
 	<string>LaunchScreen</string>
 	<key>UIRequiredDeviceCapabilities</key>