Automatic merge of T1.5.1-482-g7f7dd9993 and 8 pull requests

- Pull request #570 at 7269d24: Experimental glTF 2.0 support with PBR lighting
- Pull request #757 at d9d75f4: Unify RailDriver code implementations
- Pull request #799 at dc03850: Consolidated wind simulation
- Pull request #821 at cc3af66: Adds suppression of safety valves
- Pull request #829 at 434af02: Improvements for air brakes #3 - Emergency valves
- Pull request #839 at d00beb9: First phase of https://blueprints.launchpad.net/or/+spec/additional-cruise-control-parameters
- Pull request #842 at 9c2724d: Set up ability for steam locomotives to have multiple engines
- Pull request #845 at 2ecc164: Save axle integrator status

Source/Orts.Simulation/Simulation/RollingStocks/SubSystems/PowerTransmissions/Axle.cs

@@ -696,6 +696,8 @@ public void Restore(BinaryReader inf)
             previousSlipSpeedMpS = inf.ReadSingle();
             AxleForceN = inf.ReadSingle();
             AxleSpeedMpS = inf.ReadSingle();
+            NumOfSubstepsPS = inf.ReadInt32();
+            integratorError = inf.ReadSingle();
         }
 
         /// <summary>
@@ -708,6 +710,8 @@ public void Save(BinaryWriter outf)
             outf.Write(previousSlipSpeedMpS);
             outf.Write(AxleForceN);
             outf.Write(AxleSpeedMpS);
+            outf.Write(NumOfSubstepsPS);
+            outf.Write(integratorError);
         }
 
         /// <summary>