Make current sorting explicit / adding custom sorting of results

[hugolio]

It would be good to show how the results are sorted (currently: by date), and to provide a dropdown menu to adapt the sorting if necessary.

[hugolio]

Based on M. Wilson, Search User Interface Design (2011), design recommendation: "Give searchers control over the way results are ordered." and "Make sure it is obvious exactly how results are ordered and which, therefore, are most important."