change list sorting by user option and url parameter

[svenbolte]

It would be great to have a shortcode option usersort="1" that will display a dropdown list of available sort options.
When user selects a sort option: like "modified date desc" the list will be reloaded using new sort parameters.

Sorting could be given as an url parameter probably: ?sort=modifieddate&order=desc

screening the source code i could not find the php file where to place the logic (e.g. where the sorting is done loading the list)