Automatic merge of T1.5.1-905-gaf8fb30c5 and 13 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 9c456aa: Blueprint/train car operations UI window
- Pull request #885 at 8f94333: 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 9bead33: Downloading route content (Github, zip)
- Pull request #911 at 6834af0: docs: Add refactoring as a special type of PR
- Pull request #916 at 992cc97: Distributed Power Air Brake Synchronization
- Pull request #919 at 7aafe02: Added mouse wheel support for controls which can be moved by pressing t…
- Pull request #920 at a94e403: Update RailDriver in Manual

Author: openrails-bot

Source/Orts.Simulation/Simulation/RollingStocks/MSTSLocomotive.cs

@@ -2777,7 +2777,9 @@ protected virtual void UpdateCompressor(float elapsedClockSeconds)
             bool syncCompressor = false;
 
             // Compressor synchronization is ignored if 5 psi above the high setpoint
-            if (MainResPressurePSI < MaxMainResPressurePSI + 5.0f && LocomotivePowerSupply.AuxiliaryPowerSupplyState == PowerSupplyState.PowerOn)
+            // Only accept synchronization if MU cable is connected and locomotive power supply is on
+            if (RemoteControlGroup != -1 && MainResPressurePSI < MaxMainResPressurePSI + 5.0f 
+                && LocomotivePowerSupply.AuxiliaryPowerSupplyState == PowerSupplyState.PowerOn)
             {
                 foreach (List<TrainCar> locoGroup in Train.LocoGroups)
                 {
@@ -2786,7 +2788,7 @@ protected virtual void UpdateCompressor(float elapsedClockSeconds)
                     foreach (TrainCar locoCar in locoGroup)
                     {
                         if (locoCar is MSTSLocomotive loco)
-                            syncCompressor |= (locoGroup.Contains(this as TrainCar) || (CompressorIsMUControlled && loco.CompressorIsMUControlled))
+                            syncCompressor |= loco.RemoteControlGroup != -1 && (locoGroup.Contains(this as TrainCar) || (CompressorIsMUControlled && loco.CompressorIsMUControlled))
                                 && loco.CompressorIsOn && loco.MainResPressurePSI < loco.MaxMainResPressurePSI;
 
                         // No need to check repeatedly if we already know to sync compressors