Add convience method to await button click (sharpbrick#78)

- Add to steering calibration example

Closes sharpbrick#68 non-breaking

Author: tthiery

examples/SharpBrick.PoweredUp.Examples/ExampleCalibrationSteering.cs

@@ -16,10 +16,11 @@ public override async Task ExecuteAsync()
 
                 var calibration = ServiceProvider.GetService<LinearMidCalibration>();
                 await calibration.ExecuteAsync(motor);
+                await technicMediumHub.WaitButtonClickAsync();
 
-                await Task.Delay(5000);
                 await motor.GotoAbsolutePositionAsync(CW * 50, 20, 100, SpecialSpeed.Hold, SpeedProfiles.AccelerationProfile);
-                await Task.Delay(5000);
+                await technicMediumHub.WaitButtonClickAsync();
+
                 await motor.GotoAbsolutePositionAsync(CCW * 50, 20, 100, SpecialSpeed.Hold, SpeedProfiles.AccelerationProfile);
                 await Task.Delay(5000);
 

src/SharpBrick.PoweredUp/Hubs/Hub_Properties.cs

@@ -160,6 +160,20 @@ await Protocol.SendMessageAsync(new HubPropertyMessage()
             await RequestHubPropertySingleUpdate(property);
         }
 
+        public async Task WaitButtonClickAsync()
+        {
+            var awaitable = ButtonObservable
+                .Where(x => x == true)
+                .FirstAsync()
+                .GetAwaiter();
+
+            await SetupHubPropertyNotificationAsync(HubProperty.Button, true);
+
+            await awaitable;
+
+            await SetupHubPropertyNotificationAsync(HubProperty.Button, false);
+        }
+
         private void OnHubPropertyMessage(HubPropertyMessage hubProperty)
         {
             if (hubProperty.Property == HubProperty.AdvertisingName && hubProperty is HubPropertyMessage<string> advData)