Ghost UI to XAML and minor cleanup (#4637)

* Remove unused class, clean up XAML

* Move GhostGui.cs into UI folder and namespace

* GhostTargetWindow to seperate file

* GhostTargetWindow to XAML

* Center request button

* Improve UI, localisation

Content.Client/Ghost/Roles/UI/GhostRolesWindow.xaml.cs

@@ -12,8 +12,8 @@ namespace Content.Client.Ghost.Roles.UI
 
         public void ClearEntries()
         {
-            EntryContainer.DisposeAllChildren();
             NoRolesMessage.Visible = true;
+            EntryContainer.DisposeAllChildren();
         }
 
         public void AddEntry(GhostRoleInfo info)