Bug 23308: Change html to filter to $raw

Bug 23308: Change html to filter to $raw

This patch changes the erroneous html filter to $raw

Test plan:
- Apply patch
- Enter some HTML into the OpacMaintenanceNotice syspref
- View the OPAC front page
=> TEST: Observe that the notice displays correctly and the HTML is not
escaped

Signed-off-by: Maryse Simard <maryse.simard@inlibro.com>
Signed-off-by: frederik chenier <frederik.chenier@inlibro.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>