Bug 31450: Make additional contents publication date required

HTML customizations and news will not display without a publication
date, so we should make it required. This patch adds client-side
validation of the field to check that it's filled.

To test, apply the patch and go to Tools -> News (or HTML
customizations, or Pages).

- Click "New entry"
- Try to submit this new entry without entering a publication date.
- You should be prevented from submitting the form.
- Fill in the publication date and confirm that the form submits
  correctly.

Sponsored-by: Athens County Public Libraries
Signed-off-by: Brendan Lawlor <blawlor@clamsnet.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>

koha-tmpl/intranet-tmpl/prog/en/modules/tools/additional-contents.tt

@@ -220,7 +220,7 @@
         [% END %]
     </div>
 
-    <form id="add_additional_content" method="post" action="/cgi-bin/koha/tools/additional-contents.pl" class="validate">
+    <form id="add_additional_content" method="post" action="/cgi-bin/koha/tools/additional-contents.pl" class="validated">
         [% INCLUDE 'csrf-token.inc' %]
         <input type="hidden" name="op" value="cud-add_validate" />
         <input type="hidden" name="category" value="[% category | html %]" />
@@ -260,8 +260,9 @@
                     </li>
                 [% END %]
                 <li>
-                    <label for="from">Publication date: </label>
-                    <input id="from" type="text" name="published_on" size="15" value="[% additional_content.published_on | html %]" class="flatpickr" data-date_to="to" />
+                    <label for="from" class="required">Publication date: </label>
+                    <input id="from" type="text" name="published_on" size="15" value="[% additional_content.published_on | html %]" class="flatpickr" data-date_to="to" required="required" class="required" />
+                    <span class="required">Required</span>
                     <div class="hint">[% INCLUDE 'date-format.inc' %]</div>
                 </li>
                 <li>