shell: set the window name and icon when opening an embedded settings panel

This involves storing the default window title and icon name and resetting
the title and icon name when an embedded settings panel is closed.

The icon name and title for each panel is retrieved from the desktop file
information and stored in the CcShellModel.

shell/cc-shell-model.h

@@ -61,6 +61,7 @@ enum
   COL_PIXBUF,
   COL_CATEGORY,
   COL_SEARCH_TARGET,
+  COL_ICON_NAME,
 
   N_COLS
 };