Bug 19108: Fix Stored XSS in classsources.pl

Bug 19108: Fix Stored XSS in classsources.pl

Fixed for both Classification sources & Classification filing rules

To Test
1. first case classification source: Hit the page
   /cgi-bin/koha/admin/classsources.pl?op=add_source
   second case classification filing rules:
   Hit the page /cgi-bin/koha/admin/classsources.pl?op=add_sort_rule
2. Add a text in the field Description that contains js
3. Save the page.
4. Notice js is execute
5. Apply patch and reload, the js is escaped

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>