Allow using the ontology search as filter of ontologies

This is a small change in the ontology search for allowing the usage of the search bar in the Ontologies tab as a filter of ontologies. This is achieved by showing all ontologies in a paginated view when no keywords are typed.

The unit tests have been properly updated.

The refactoring of the search library to make keyword suggestion and search faster is being dealt with in a separate branch named correcting380_suggesting_keywords_faster (Issue #380).