Show overall course visibility in navbar

A few versions ago, moodle replaced the old "grayed-out" look of hidden items with tags which show detailed information about the visibility/accessibility of activities or topics. However, the status of the main visibility switch - course visibility - is still not displayed anywhere on the course site.

It would greatly improve clarity of design if the overall course visibility was displayed directly in the navbar when viewing a course, as teachers often forget to set their courses from "hide" to "show" once they are done editing them.

Discussion was started here: https://moodle.org/mod/forum/discuss.php?d=368581