WebSearch: anyfield in CFG_WEBSEARCH_SYNONYM_KBRS

• CFG_WEBSEARCH_SYNONYM_KBRS can use the keyword 'anyfield' to match a given knowledge base when searching without a particular field. (closes #1493)

Signed-off-by: Jerome Caffaro <jerome.caffaro@cern.ch>
Reviewed-by: Ludmila Marian <ludmila.marian@cern.ch>