Bug 24473: Add $raw filter for Syndetics content

Bug 24473: Add $raw filter for Syndetics content

Syndetics offers enhanced content in the OPAC under the tabs 'Title Notes',
'Excerpt', 'About the author', 'Editions'. They provide this info as HTML
therefore we should filter it as $raw so the content shows up without the markup.

Signed-off-by: Stina Hallin <stina.hallin@ub.lu.se>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 6b9572e0c8fb9f1ad1e60ed5db50e69c60ac1a00)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>