More regression bugfixes relating to last version. Mainly to do with lists.

• Miner : load existing query, could not modify entity if query loaded contained only one item. Now fixed
• Unit purchase: clicking on modify in resale list crashed c9.  (Actually bug has been there for a while)
• Unit purchase: resale list buttons now disable/enable depending on content of list and selected item
• Focusability of lists without any rows.  Prior version switched back to c8 model, empty lists are focusable.  But there is merit in c9's prior approach of skipping over empty lists.  Implemented compromise solution; Database driven lists are focusable when empty, whereas other lists, such as tree lists and memory lists (like unit purchase line items) are not focusable.