Bug 20891: Escape list's names in JSON

Bug 20891: Escape list's names in JSON

When someone uses \ in the description of a list, the datatable in staff
won't load and keeps processing.

Test plan:
- Create a list named "<script>alert('hola');</script>"
- Create another list named "k\o\h\a"
- Hit /cgi-bin/koha/virtualshelves/shelves.pl

=> Without this patch the lists will not be displayed, JSON is
malformated
=> With this patch everything is ok

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>