search: new Query class
- Renames SearchEngine class to Query that better describes its function.
- NEW Adds new API for querying records.
- INCOMPATIBLE Removes support for legacy perform_request_search and search_unit API functions.
Reviewed-by: Tibor Simko <tibor.simko@cern.ch>
Signed-off-by: Jiri Kuncar <jiri.kuncar@cern.ch>