Use protobuf to generate websocket JSON

Manually generating the JSON was getting to be painful, use protobuf's
JSON generator.

Change-Id: Id387ae9745de2e744d602f4fbec606f6ba1364bc
diff --git a/y2019/vision/server/www/generate_camera.cc b/y2019/vision/server/www/generate_camera.cc
index 8e516c3..757ce69 100644
--- a/y2019/vision/server/www/generate_camera.cc
+++ b/y2019/vision/server/www/generate_camera.cc
@@ -15,6 +15,8 @@
   out_file << "export const CAMERA_POSES = [\n";
   for (size_t ii = 0; ii < constants::Values::kNumCameras; ++ii) {
     out_file << "    ";
+    // TODO(james): Decide how to manage visualization for practice and code
+    // bots.
     DumpPose(&out_file,
              GetCamera(CameraSerialNumbers(CompBotTeensyId())[ii])->geometry);
     out_file << ",\n";