Add more sort options to the widgets interface

[johnh]

Search results can be sorted by Title, Relevance etc. Other options that users may wish to use are:

Title (Z-A), Category (A-Z), Category (Z-A), Change date (earliest first), Change date (latest first), Organisation (A-Z), Organisation (Z-A), Resource type (A-Z), Resource type (Z-A).

I would be nice if these were available in the widget interface or easily added by a list in the database.