Added selection/deselection of items to DataViews (APPWTV25)

Navigation: added selection/deselection of items to DataViews - APPWTV25  
Two new functions added to ui.browse: toggleSelectItem and deselectItem  
They are bound to S and D keys (lowercase)  
Functions check whether a column is masked or not.  
*TODO:* navigation/selection logic for playlists and for the segmented button (last column)