Update LiveWindow to provide continuous telemetry. (#771)

LiveWindow.updateValues() is now called from IterativeRobotBase on every
loop iteration.  Telemetry for all WPILib classes is enabled by default;
it can be disabled for specific classes using LiveWindow.disableTelemetry(),
or all telemetry can be disabled using LiveWindow.disableAllTelemetry().

This necessitated changing the hook methodology into other classes to
be more property-based rather than each class providing multiple functions.
This had the benefit of reducing boilerplate and increasing consistency.

- Remove NamedSendable, add name to Sendable.

- Provide SendableBase abstract class.

- Deprecate LiveWindow addSensor/addActuator interfaces.

- Add LiveWindow support to drive classes.

- Add addChild() helper functions to Subsystem.

- Fix inheritance hierarchy.  Now only sensors inherit from SensorBase.
  Other devices inherit from some combination of SendableBase, ErrorBase, or
  nothing.

wpilibc/src/main/native/cpp/AnalogPotentiometer.cpp

@@ -8,6 +8,7 @@
 #include "AnalogPotentiometer.h"
 
 #include "ControllerPower.h"
+#include "SmartDashboard/SendableBuilder.h"
 
 using namespace frc;
 
@@ -23,9 +24,11 @@ using namespace frc;
  */
 AnalogPotentiometer::AnalogPotentiometer(int channel, double fullRange,
                                          double offset)
-    : m_analog_input(std::make_unique<AnalogInput>(channel)),
+    : m_analog_input(std::make_shared<AnalogInput>(channel)),
       m_fullRange(fullRange),
-      m_offset(offset) {}
+      m_offset(offset) {
+  AddChild(m_analog_input);
+}
 
 /**
  * Construct an Analog Potentiometer object from an existing Analog Input
@@ -76,26 +79,9 @@ double AnalogPotentiometer::Get() const {
  */
 double AnalogPotentiometer::PIDGet() { return Get(); }
 
-/**
- * @return the Smart Dashboard Type
- */
-std::string AnalogPotentiometer::GetSmartDashboardType() const {
-  return "Analog Input";
-}
-
 /**
  * Live Window code, only does anything if live window is activated.
  */
-void AnalogPotentiometer::InitTable(
-    std::shared_ptr<nt::NetworkTable> subtable) {
-  if (subtable) {
-    m_valueEntry = subtable->GetEntry("Value");
-    UpdateTable();
-  } else {
-    m_valueEntry = nt::NetworkTableEntry();
-  }
-}
-
-void AnalogPotentiometer::UpdateTable() {
-  if (m_valueEntry) m_valueEntry.SetDouble(Get());
+void AnalogPotentiometer::InitSendable(SendableBuilder& builder) {
+  m_analog_input->InitSendable(builder);
 }