Allow the sorting of the collection to be more user defined

Currently Sorting of the collection is very limited in scope as it only allows you to change the first part that is sorted and then does the second level as Artist. Some people do not even use artist to sort while others want to be able to use date or rate.

This is done in Amarok by giving a complex menu to do this. Hopefully there is a more simple way for doing this but it would be wonderful to see this kind of customization available.