Automatic merge of T1.5.1-922-g0a17d985e and 15 pull requests

- Pull request #570 at 3539862: Experimental glTF 2.0 support with PBR lighting
- Pull request #839 at d00beb9: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #876 at f92de76: docs: add source for documents previously on website to source Documentation folder
- Pull request #882 at 3ca0eb1: Blueprint/train car operations UI window
- Pull request #885 at 03d4a52: feat: Add notifications to Menu
- Pull request #886 at 6c0785b: Scene viewer extension to TrackViewer
- Pull request #892 at 1f5ba4c: Signal Function OPP_SIG_ID_TRAINPATH
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #903 at 29f3d1a: Downloading route content (Github, zip)
- Pull request #912 at f7b85e4: New Triple Valve Features Vol. 2
- Pull request #919 at 26cc6a8: Added mouse wheel support for controls which can be moved by pressing t…
- Pull request #923 at e0f3c55: Add curve squeal to route
- Pull request #924 at 6c2c3cd: Default Asset Improvements
- Pull request #925 at e3b1688: Fix brakeshoe force bug
- Pull request #927 at cf687d4: AI Train Power Supply/Lights Fix

Author: openrails-bot

Source/Menu/Notifications/NotificationManager.cs

@@ -251,6 +251,8 @@ private Check CheckExcludes(Check check)
                             if (SystemInfo.Application.Version.IndexOf(c.Value, StringComparison.OrdinalIgnoreCase) > -1)
                                 return check;
                             break;
+                        case "already updated": // ReplaceParameter() changed {{new_version}} to "already updated"
+                            break;
                         case "system":
                             var os = SystemInfo.OperatingSystem;
                             var system = $"{os.Name} {os.Version} {os.Architecture} {os.Language} {os.Languages ?? new string[0]}";
@@ -380,9 +382,10 @@ private string ReplaceParameter(string field)
                 case "new_version":
                     replacement = UpdateManager.LastUpdate == null 
                         || UpdateManager.ChannelName == ""
-                        || UpdateManager.LastUpdate.Version == SystemInfo.Application.Version
-                        ? "none"
-                        : UpdateManager.LastUpdate.Version;
+                        ? "not available"
+                        : UpdateManager.LastUpdate.Version == SystemInfo.Application.Version
+                            ? "already updated"
+                            : UpdateManager.LastUpdate.Version;
                     break;
                 case "release_date":
                     replacement = UpdateManager.LastUpdate == null