navbar: Show realm icon logo instead of full logo on narrow widths.

When left sidebar is hidden between 1200px and 768px, we show
smaller realm icon logo instead of the full realm logo. Also,
we use the new space to expand the middle column to better show
the narrow description.

web/src/ui_init.js

@@ -166,6 +166,7 @@ function initialize_navbar() {
     const rendered_navbar = render_navbar({
         embedded: page_params.narrow_stream !== undefined,
         user_avatar: current_user.avatar_url_medium,
+        realm_icon_url: realm.realm_icon_url,
     });
 
     $("#header-container").html(rendered_navbar);