PWM: Use getRaw and setRaw for Sendable "Value" property. (#963)

Also change type to "PWM".  Move old PWM Sendable behavior for both value
and type to PWMSpeedController.

wpilibc/src/main/native/include/PWMSpeedController.h

@@ -28,6 +28,7 @@ class PWMSpeedController : public SafePWM, public SpeedController {
 
  protected:
   explicit PWMSpeedController(int channel);
+  void InitSendable(SendableBuilder& builder) override;
 
  private:
   bool m_isInverted = false;