Add support for query collation information

* src/VuFindSearch/Backend/Solr/Response/Json/QuerySuggestion.php: New
  class. Query suggestion data object.

* src/VuFindSearch/Backend/Solr/Response/Json/Spellcheck.php
(addQuerySuggestion): New function. Add a query suggestion.
(getQuerySuggestions): New function. Return query suggestions.
(__construct): Process query suggestions.