WebSearch: re-enabled basic search cache
- Enabled the search results cache back again. It is used now for simple search queries only and for search stages 1-3 only. In order to plug the cache for more search stages, or for advanced search queries too, a small refactoring of perform_request_search() would be profitable first.
- Changed collection reclist, I18N name and field I18N name caches to use the DataCacher class. Cleaned away unused caching functions.
- Optimized retrieval of collection and field I18N names in search engine's HTML output, speeding up search engine considerably if one has hundreds of collections defined.
- Changed DataCacher API (better names). Exposes cache internals, which is not too ideal. We may want to create special list/dict/lazy data cacher subclasses one day.
- Updated DataCacher clients as per the API change.