[Kst] Extended selection mode for editmultiplewidget

[Brisset, Nicolas]

>   It's for click selection vs add-to-selection.  With 
> Extended you have to hold CTRL to add items to a selection, 
> and shift to select contiguous regions.  With Multi you can 
> just click on items to toggle them on/off in the selection.
Though I agree that the extra keystroke for small selections (2 or 3
items) is not ideal, there are two reasons why I much prefer Extended:
- in Multi mode, adding long lists is *very* tedious (1 click per item
!)
- users are so used to Extended from other applications/environments
(including MS Windows) that anything else tends to confuse them