WebSearch: date after, date before bug fix

* Fixes the following bug:
    DATE AFTER XXXX is interpreted
    * year .GT. xxxx in Spires
    * year .GE. xxxx in Inspires

* Fixes unit tests for date after/before queries.
* Deletes a duplicate unit test for 'find date 1976-04'.
* Adds unit tests for 'find date < 1978-10'.
* Adds unit tests for 'find date > 1978-10'.
* Adds unit tests for 'find date 23 Sep 2010'.
* Adds unit tests for 'find (date 23 Sep 2010)'. The parenthesis after the date is an edge case for the regexp used by th method 'convert_date'.
* Fixes method '_convert_spires_date_after_to_invenio_span_query'.
* Fixes method '_convert_spires_date_before_to_invenio_span_query'.
* Fixes regexp used by '_convert_all_dates'.
* Fixes indentation for kwalitee.