Bug 26664: Fix sorting for date last seen in inventory tool

This adds the standard datatable sorting for dates to the inventory
table as described here:
https://wiki.koha-community.org/wiki/DataTables_HowTo#Sorting_dates_regardless_of_date_format_preference

To test:
- Go to the inventory tool
- Search for a big sample list of items with different date last seen
- Sort the table now by "date last seen" by clicking on the table header cell
- Try different settings of the DateFormat system preferences
- Verify sorting is incorrect (alphabetic, not by date)
- Apply patch
- Repeat testing and very all is sorting correctly now

Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>

koha-tmpl/intranet-tmpl/prog/en/modules/tools/inventory.tt

@@ -200,7 +200,7 @@
             <th>Lost</th>
             <th>Damaged</th>
             <th>Withdrawn</th>
-            <th>Last seen</th>
+            <th class="title-string">Last seen</th>
             <th>Problems</th>
         </tr>
     </thead>
@@ -239,7 +239,7 @@
             [% result.withdrawn | html %]
             </td>
             <td>
-            [% result.datelastseen | $KohaDates %]
+                <span title="[% result.datelastseen %]">[% result.datelastseen | $KohaDates%]</span>
             </td>
             <td>
             [% FOREACH problem IN result.problems %]
@@ -350,6 +350,7 @@
                     "aoColumnDefs": [
                         { "sType": "anti-the", "aTargets" : [ "anti-the" ] },
                         { "bSortable": false, "bSearchable": false, "aTargets": [ 0 ] },
+                        { "sType": "title-string", "aTargets" : [ "title-string" ] },
                     ],
                     // 3rd column is callnumber
                     "aaSorting": [[ 2, "asc" ]],