Section menu for the lazy blogger

Section menu for the lazy blogger

The current menu system works great, but is too much work if all you want is a simple menu with the sections as menu items, and having these menu items connected to the pages in a way that enables setting the correct menu item as active for both the section lists and the pages itself.

This commit adds a new option `SectionPagesMenu' which, if set, will create a new menu with that name with all the sections as menu items. The pages in the sections will behave as "shadow members" of these section items as `blogpage.HasMenuCurrent "sectionmenu" $sectionmenuitem` will return true.

If a menu item with the same `identifier` is defined in site config, *that* item will take precedence.