Consider additional filters or facets for the advanced search

[nemobis]

While #696 deals with the main search field, I think a separate project would be to add some features to the advanced search. I think this is actually easier because it can be done without changing anyone's default experience.

Use case: as an interested Dissemin user, when I search for the publications of some prolific authors like Eric Lander, I want options to filter the list of search results in order to see a group of results most likely to contain what I'm interested in (e.g. to pick some works which are easy targets for deposit by an author, or to see how many "relevant" works are OA).

Possible ideas: filter (or rank?) by position of the author, allowing to quickly find the works for which the author is a "main" author. Some DSpace repositories allow to search by first author, as far as I know, but that's pretty hidden and/or available only for some records (controlled records?). Example searches in two DSpace: air.unimi.it, dspace.mit.edu with authority or by name.