Enabling and disabling items from an archived menu

The Presentation framework calls HandleCurrentSelectionChange whenever the user makes a new selection. TTilesPresenter::HandleCurrentSelectionChange sets the enabled state on the Red, Blue, and Green menu items based on whether the new selection is empty. The items are only enabled if at least one tile is selected. The items for adding new tiles are always enabled because the command underlying these items, TCreateTileCommand, acts directly on the model and doesn't rely on selected data, as described in "Implementing TCreateTileCommand" on page 90.