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