Automatic merge of T1.5.1-776-g362e836a2 and 16 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 a055bca: Blueprint/train car operations UI window
- Pull request #885 at d9ce84b: 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 #893 at bf8876b: Signal errors
- Pull request #894 at 5ff1e73: Correct Decrease Colour
- Pull request #896 at 5866028: First implementation of https://blueprints.launchpad.net/or/+spec/specific-sounds-for-ai-trains
- Pull request #897 at 0a9d939: feat: Improved system information collection
- Pull request #899 at e5db0a2: Duplex steam engines - Booster Engine addition
- Pull request #903 at a0d2991: first phase downloading from Github
- Pull request #904 at 71beb33: fix: adds downgrade to low precision
- Pull request #906 at 0e0aa8b: Bug fix for https://bugs.launchpad.net/or/+bug/2047299 Crash loading a 3Dcab-only loco
- Pull request #907 at 54d1119: Bug fix for https://bugs.launchpad.net/or/+bug/2047300 Dynamic tracks disappear after long tunnel

Author: openrails-bot

Source/RunActivity/Viewer3D/DynamicTrack.cs

@@ -710,6 +710,17 @@ public static PitchControls GetPitchControl(string sPitchControl)
 
             }
         }
+
+        /// <summary>
+        /// Marks the generic track profile, so that its textures never get deleted
+        /// </summary>
+        [CallOnThread("Loader")]
+        public void Mark()
+        {
+            foreach (LOD lod in LODs)
+                lod.Mark();
+        }
+
     }
 
     public class LOD

Source/RunActivity/Viewer3D/World.cs

@@ -116,6 +116,8 @@ public void Load()
                     Precipitation.Mark();
                     Terrain.Mark();
                     Scenery.Mark();
+                    Viewer.TRP?.TrackProfile?.Mark();
+                    Viewer.TRP?.TrackProfileTun?.Mark();
                     Trains.Mark();
                     RoadCars.Mark();
                     Containers.Mark();