Bug 29463: Escape utf8 characters before appending search query to url

Bug 29463: Escape utf8 characters before appending search query to url

To test:
1) go to the main page of Koha and search in the "Check out" search window type "näyttö".
2) see that umlauts got replaced with replacement characters.
3) apply the patch.
4) repeat 1-2, ensure that umlauts displayed correctly and are not getting replaced with replacement characters.

JK: remove period from commit title
Signed-off-by: Joonas Kylmälä <joonas.kylmala@iki.fi>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>