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/GyroBase.cpp

@@ -7,7 +7,7 @@
 
 #include "GyroBase.h"
 
-#include "LiveWindow/LiveWindow.h"
+#include "SmartDashboard/SendableBuilder.h"
 #include "WPIErrors.h"
 
 using namespace frc;
@@ -29,21 +29,7 @@ double GyroBase::PIDGet() {
   }
 }
 
-void GyroBase::UpdateTable() {
-  if (m_valueEntry) m_valueEntry.SetDouble(GetAngle());
-}
-
-void GyroBase::StartLiveWindowMode() {}
-
-void GyroBase::StopLiveWindowMode() {}
-
-std::string GyroBase::GetSmartDashboardType() const { return "Gyro"; }
-
-void GyroBase::InitTable(std::shared_ptr<nt::NetworkTable> subTable) {
-  if (subTable) {
-    m_valueEntry = subTable->GetEntry("Value");
-    UpdateTable();
-  } else {
-    m_valueEntry = nt::NetworkTableEntry();
-  }
+void GyroBase::InitSendable(SendableBuilder& builder) {
+  builder.SetSmartDashboardType("Gyro");
+  builder.AddDoubleProperty("Value", [=]() { return GetAngle(); }, nullptr);
 }