UI: Fix datepicker vs. redactor toolbar z-index issue

Tested with 1.9.4 - found no other / related / new issues due to this change of the z-index.

Fixes: https://github.com/osTicket/osTicket-1.8/issues/980
Fixes: https://github.com/osTicket/osTicket-1.8/issues/1411

css/redactor.css

@@ -327,7 +327,7 @@ body .redactor_box_fullscreen {
   background: #fff;
   border: none;
   box-shadow: 0 1px 2px rgba(0, 0, 0, 0.2);
-  z-index: 3;
+  z-index: 1;
 }
 .redactor_toolbar:after {
   content: "";