Site navigation bar

Adds a Toolbar for site navigation using the rel- or rev-attribute of Link- and a-elements. A context menu has been added to the navigation bars menuitems.The navigation bar is now customizable, you can select Between the classical appearance like in Mozilla-Suite and an configuration where all menus appear on the navigation bar.On the other hand you can customize the appearance by dragging the elements onto other bars e.g. the Menu-Bar using the toolbox context menu and selecting `customize...`.You can select differend modi to display the navigation bar. This allows you to display the navigation bar either in the toolbox or in the statusbar or as a menu in the menubar or in the `Extra`-menu.