Add FRC Driver Station connection support.

The 2017 FRC Driver Station supports getting the robot IP via a TCP
connection that returns JSON.  Use this to support overriding the
server IP address used for client connections.

Default to using this approach for client connections in the NetworkTable
interfaces.

Add support for setting the server address without stopping and
restarting the client.

SetTeam now also round-robins by default.

src/DsClient.h

@@ -0,0 +1,38 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) FIRST 2016. 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.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#ifndef NT_DSCLIENT_H_
+#define NT_DSCLIENT_H_
+
+#include "support/atomic_static.h"
+#include "support/SafeThread.h"
+
+namespace nt {
+
+class DsClient {
+ public:
+  static DsClient& GetInstance() {
+    ATOMIC_STATIC(DsClient, instance);
+    return instance;
+  }
+  ~DsClient() = default;
+
+  void Start(unsigned int port);
+  void Stop();
+
+ private:
+  DsClient() = default;
+
+  class Thread;
+  wpi::SafeThreadOwner<Thread> m_owner;
+
+  ATOMIC_STATIC_DECL(DsClient)
+};
+
+}  // namespace nt
+
+#endif  // NT_DSCLIENT_H_