GTableView and friends: API improvements for 'Sortable' flag.

Author: https://github.com/ignas-sa
Commit: 6228e18a09
Pull-request: https://github.com/SerenityOS/serenity/pull/442
Reviewed-by: https://github.com/awesomekling

Libraries/LibGUI/GDirectoryModel.cpp

@@ -119,7 +119,7 @@ GModel::ColumnMetadata GDirectoryModel::column_metadata(int column) const
 {
     switch (column) {
     case Column::Icon:
-        return { 16, TextAlignment::Center, false };
+        return { 16, TextAlignment::Center, nullptr, GModel::ColumnMetadata::Sortable::False };
     case Column::Name:
         return { 120, TextAlignment::CenterLeft };
     case Column::Size: