Add 'New Update' notification flow

Introduce a small update-notification feature: add AppEvents.HasUpdateNotified event and have TaskManager publish it when update messages exist. Add localized resource key (menuNewUpdate) and expose it in the ResUI designer; update resource files for several languages. In the UI, add a New Update button in MainWindow.xaml, wire its click to the existing check-update handler, bind its visibility to a new BlNewUpdate property on MainWindowViewModel, and subscribe the viewmodel to the new event. Also reset the notification flag after showing the Check Update dialog.

v2rayN/v2rayN.Desktop/Views/MainWindow.axaml

@@ -102,6 +102,13 @@
 
                     <MenuItem x:Name="menuClose" Header="{x:Static resx:ResUI.menuExit}" />
                 </Menu>
+
+                <Button
+                    x:Name="btnNewUpdate"
+                    Margin="{StaticResource MarginLr8}"
+                    HorizontalAlignment="Left"
+                    Content="{x:Static resx:ResUI.menuNewUpdate}"
+                    IsVisible="False" />
             </DockPanel>
 
             <view:StatusBarView DockPanel.Dock="Bottom" />