WebSearch: index-time and search-time synonyms

• New index-time and search-time synonym facility, taking care of synonyms in user searches. The synonym terms are defined in knowledge bases and can be specified per index. The index-time synonyms are governed by CFG_BIBINDEX_SYNONYM_KBRS and synonym terms are stored in the index. The search-time synonyms are governed by CFG_WEBSEARCH_SYNONYM_KBRS and are looked up on-the-fly during query time. The second facility is therefore slower and useful for more `volatile' style of synonym lists, such as most often made typos; these synonym terms are not offered in the browse interface or as nearest terms suggestions. (closes #505)

• Adds two new demo synonym KBs and corresponding regression tests.

• Note: will need some amendments WRT forthcoming pair index searching.