minor changes

* lbxVisits databind datetime format -
http://blogs.msdn.com/b/vsdata/archive/2009/07/07/customize-format-of-datetime-string-in-wpf-and-winform-data-binding.aspx
* button enabled based on listbox selectedindex -
http://stackoverflow.com/questions/17906/enabling-a-button-in-wpf-depending-on-listbox-selectedindex
* double click to open