Should we show an error message when an empty search is done?

[martindholmes]

At the moment, if a search is done with no search text and no filter selections, we just report zero documents found. This isn't really intuitive. There are two options:

1. Find all of the documents in the collection. For small collections, this would just result in the display of links to all documents, and might be a useful thing. For larger collections, it would just report the total number of documents as an excessive result.
2. Show an error message to the effect that no search text or filters have been configured.