constify and deautoify more things in vision

This was part of my effort to understand how things work.

Change-Id: I49dae7400fba8ec1f02d006f3d14c6dc254a8187
diff --git a/y2019/vision/target_finder.h b/y2019/vision/target_finder.h
index 666ae2f..1ba79ba 100644
--- a/y2019/vision/target_finder.h
+++ b/y2019/vision/target_finder.h
@@ -73,7 +73,7 @@
   aos::vision::AnalysisAllocator alloc_;
 
   // The template for the default target in the standard space.
-  Target target_template_;
+  const Target target_template_;
 
   IntrinsicParams intrinsics_;