Add getters on velocity message

Author: Douglasdc3

src/main/java/aero/t2s/modes/decoder/df/df17/AirborneVelocityGroundspeed.java

@@ -93,4 +93,20 @@ public void apply(Track track) {
                 .setVy(yVelocity);
         }
     }
+
+    public boolean isVxAvailable() {
+        return xVelocityAvailable;
+    }
+
+    public int getVx() {
+        return xVelocity;
+    }
+
+    public boolean isVyAvailable() {
+        return yVelocityAvailable;
+    }
+
+    public int getVy() {
+        return yVelocity;
+    }
 }