dhb Medialist : created context menu function and moved lines which create

     the context menu function there.  Call this function from
     MediaList::PgSeltreeWidgetClicked() so that the menu items only get added
     once instead of every time the tree gets repopulated.  Otherwise the popup
     menu ends up with repeats.
     Joblist : Set all flags of the table items to 0 so that the defaults of
     editable are not active.