New CMS visibility settings (#12940)

TNL-4906 Subsections now use radio buttons, to allow for "hide after due" as a
visibility option. Also, all tabs have been consolidated to "Basic" and
"Advanced", and visibility options have moved there.

Documentation links are updated to assist course authors with the new
visibility options. Tests have also been updated, and the changes suggested
in TNL-4951 are included.

cms/static/js/utils/date_utils.js

@@ -52,7 +52,10 @@ function($, date, TriggerChangeEventOnEnter) {
         // given a pair of inputs (datepicker and timepicker), return a JS Date
         // object that corresponds to the datetime.js that they represent. Assume
         // UTC timezone, NOT the timezone of the user's browser.
-        var date = $(datepickerInput).datepicker("getDate"), time = null;
+        var date = null, time = null;
+        if (datepickerInput.length > 0) {
+            date = $(datepickerInput).datepicker("getDate");
+        }
         if (timepickerInput.length > 0) {
             time = $(timepickerInput).timepicker("getTime");
         }