Bug 20334: Option for escaping slashes in search queries

Bug 20334: Option for escaping slashes in search queries

Add "QueryRegexEscapeOption" system preference to provide option to escape
Elasticsearch regexp delimiters (/) within queries, or alternativly to
unescape escaped slashes (\/) while escaping unescaped slashes, in
effect making "\/" the new regexp delimiter.

How to test:
1) Run tests in ./t/Koha/SearchEngine/ElasticSearch/QueryBuilder.t
2) All tests should succeed

Signed-off-by: Nicolas Legrand <nicolas.legrand@bulac.fr>
Signed-off-by: Maksim Sen <maksim.sen@inlibro.com>
Signed-off-by: Séverine QUEUNE <severine.queune@bulac.fr>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>