Add constants for built-in Shuffleboard widgets and layouts (#1468)

Prevents users from having to remember (and correctly type) the names of Shuffleboard widgets.

wpilibc/src/main/native/cpp/shuffleboard/BuiltInWidgets.cpp

@@ -0,0 +1,35 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018 FIRST. All Rights Reserved.                             */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#include "frc/shuffleboard/BuiltInWidgets.h"
+
+using namespace frc;
+
+const WidgetType BuiltInWidgets::kTextView{"Text View"};
+const WidgetType BuiltInWidgets::kNumberSlider{"Number Slider"};
+const WidgetType BuiltInWidgets::kNumberBar{"Number Bar"};
+const WidgetType BuiltInWidgets::kDial{"Simple Dial"};
+const WidgetType BuiltInWidgets::kGraph{"Graph"};
+const WidgetType BuiltInWidgets::kBooleanBox{"Boolean Box"};
+const WidgetType BuiltInWidgets::kToggleButton{"Toggle Button"};
+const WidgetType BuiltInWidgets::kToggleSwitch{"Toggle Switch"};
+const WidgetType BuiltInWidgets::kVoltageView{"Voltage View"};
+const WidgetType BuiltInWidgets::kPowerDistributionPanel{"PDP"};
+const WidgetType BuiltInWidgets::kComboBoxChooser{"ComboBox Chooser"};
+const WidgetType BuiltInWidgets::kSplitButtonChooser{"Split Button Chooser"};
+const WidgetType BuiltInWidgets::kEncoder{"Encoder"};
+const WidgetType BuiltInWidgets::kSpeedController{"Speed Controller"};
+const WidgetType BuiltInWidgets::kCommand{"Command"};
+const WidgetType BuiltInWidgets::kPIDCommand{"PID Command"};
+const WidgetType BuiltInWidgets::kPIDController{"PID Controller"};
+const WidgetType BuiltInWidgets::kAccelerometer{"Accelerometer"};
+const WidgetType BuiltInWidgets::k3AxisAccelerometer{"3-Axis Accelerometer"};
+const WidgetType BuiltInWidgets::kGyro{"Gyro"};
+const WidgetType BuiltInWidgets::kRelay{"Relay"};
+const WidgetType BuiltInWidgets::kDifferentialDrive{"Differential Drivebase"};
+const WidgetType BuiltInWidgets::kMecanumDrive{"Mecanum Drivebase"};
+const WidgetType BuiltInWidgets::kCameraStream{"Camera Stream"};