Improve block bounds HUD feature

* Use different material than selection box, so it doesn't break
  for non-default `node_highlighting` values.
* Add `show_block_bounds_radius_near` setting.
* Draw mesh chunk edges in a different color (red vs yellow).

src/client/hud.h

@@ -137,6 +137,7 @@ private:
 	v3f m_selected_face_normal;
 
 	video::SMaterial m_selection_material;
+	video::SMaterial m_block_bounds_material;
 
 	scene::SMeshBuffer m_rotation_mesh_buffer;