Automatic merge of T1.5.1-145-g5f2ded579 and 13 pull requests

- Pull request #652 at 918fdb1: Add button functions to Raildriver
- Pull request #706 at 570ab21: Extended door functionality
- Pull request #719 at 13a1638: Upgraded to MonoGame 3.8.0 (+ small update for other libraries)
- Pull request #722 at fb9079e: Fix Windows Forms deprecations in ActivityEditor
- Pull request #732 at 9cffa6d: Improvements for air brakes
- Pull request #740 at b3e66ca: Refactored the circuit breaker and the traction cut-off relay in order to use the same design pattern as the C# signal scripts (compatible with current scripts)
- Pull request #744 at 3c2dc07: Fixed and improved cabview control conditions related to power supply state
- Pull request #746 at 4609acb: Website release 1.5.1
- Pull request #748 at 4f0e878: latitude/longitude fix for bug 1393111
- Pull request #749 at db5764c: OpenRailway Map
- Pull request #753 at ab8fe32: Extends CabControls for user input
- Pull request #754 at 70a1325: Container weights: https://blueprints.launchpad.net/or/+spec/container-weights
- Pull request #755 at 2fd409a: Bug fix for https://bugs.launchpad.net/or/+bug/1999330 Crash with a throttle-air combined control

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

@@ -3983,7 +3983,7 @@ public void SetCombinedHandleValue(float value)
                 else if (CombinedControlType == CombinedControl.ThrottleAir && canBrake && value > CombinedControlSplitPosition)
                     SetTrainBrakeValue((MathHelper.Clamp(value, CombinedControlSplitPosition, 1) - CombinedControlSplitPosition) / (1 - CombinedControlSplitPosition));
                 else if (DynamicBrakePercent < 0 || TrainControlSystem.FullDynamicBrakingOrder ||
-                    (!CruiseControl.DynamicBrakePriority && CruiseControl.SpeedRegMode == CruiseControl.SpeedRegulatorMode.Auto))
+                    (CruiseControl !=null && !CruiseControl.DynamicBrakePriority && CruiseControl.SpeedRegMode == CruiseControl.SpeedRegulatorMode.Auto))
                     SetThrottleValue(1 - MathHelper.Clamp(value, 0, CombinedControlSplitPosition) / CombinedControlSplitPosition);
             }
         }