BibIndex: reliable tests cleanup
WebSearch: date operators `<=` and `>=`

* Replaces the SPIRES operators `<=` and `>=` with
  the Invenio operators before the equal signs removal
  and before replacing the date before/after operators

* Adds unit tests to the query parser

Signed-off-by: Federico Poli <federico.poli@cern.ch>
OPS: BibAuthorID: skip failing tests