WebSearch: query parser regexp fix

* Fixes regexp in query parser.
* Deletes a duplicate unit test for 'find date 1976-04'.
* Adds a unit test for 'find date 23 Sep 2010'.
* Adds a unit test for 'find (date 23 Sep 2010)'. The parenthesis after the date is an edge case for the regexp used by th method 'convert_date'.