Grid widget 0.2.4 - keyboard & mouse wheel support

The 0.2.4 release - keyboard navigation, mouse wheel support, bug fixes

keyboard navigation: up/down, page up/down, home/end.
added support for mouse wheel scrolling.
Ctrl-click on already selected row clears selection.
Shift-click performs block selection.
auto-scroll to make current selection visible.
setUsername and setPassword methods for XML data models.
removal of for .. in .. loops.