Add utility class tests (#871)

Checks for classes that only have static methods.

wpilibj/src/main/java/edu/wpi/first/wpilibj/RobotController.java

@@ -18,6 +18,7 @@ import edu.wpi.first.wpilibj.hal.PowerJNI;
  */
 public final class RobotController {
   private RobotController() {
+    throw new UnsupportedOperationException("This is a utility class!");
   }
 
   /**

wpilibj/src/main/java/edu/wpi/first/wpilibj/livewindow/LiveWindow.java

@@ -45,6 +45,10 @@ public class LiveWindow {
   private static boolean liveWindowEnabled = false;
   private static boolean telemetryEnabled = true;
 
+  private LiveWindow() {
+    throw new UnsupportedOperationException("This is a utility class!");
+  }
+
   public static synchronized boolean isEnabled() {
     return liveWindowEnabled;
   }

wpilibj/src/main/java/edu/wpi/first/wpilibj/smartdashboard/SmartDashboard.java

@@ -51,6 +51,10 @@ public class SmartDashboard {
     HLUsageReporting.reportSmartDashboard();
   }
 
+  private SmartDashboard() {
+    throw new UnsupportedOperationException("This is a utility class!");
+  }
+
   /**
    * Maps the specified key to the specified value in this table. The key can not be null. The value
    * can be retrieved by calling the get method with a key that is equal to the original key.