-Use QSortFilterProxyModel for filtering instead of KDirList::setFilterName

-Use QSortFilterProxyModel for filtering instead of KDirList::setFilterName
-Map DolphinView::Sorting to a column of the KDirModel and sort this column
-Reimplement QAbstractItemModel::sort(int,SortOrder) to keep track of the
 sorted column and order as dolphin uses this in the config dialogs. We will
 now work correctly if a view changes sorting.

svn path=/trunk/playground/utils/dolphin/; revision=616170