Define process flow when search field is empty. Closes #82

When the user query is empty (i.e. RequestParams.toSting() yields an empty string - this means also no filters are selected) then we do not display the search results but clean search results HTML DIV instead. However, we still execute the query (only once if caching is used) which means we get facets results and can populate all filters accordingly.
[Author filter] Move to new general list filter implementation. Closes #81