Bug 36235: Encode system preference data with encodeURIComponent

Bug 36235: Encode system preference data with encodeURIComponent

To test:
1. Add some data to a freetext system preference like IntranetUserJS or AdditionalFieldsInZ3950ResultAuthSearch that includes a semicolon;
2. Save the pref and reload the page or check the DB. Everything after the semicolon is removed.
3. Apply patch, try again. Data should remain as is.

Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>