Header accessibility and configuration improvements

[crnh]

Accessibility:

• Use a nav element instead of a div
• Add aria-current="page" attribute to the element of the current page

Configuration:

• Compare item name with the .LinkTitle attribute instead of .Name. This allows to have a different title in the menu / URL than shown on the page. For example, I have a contact page which I want to show as '/contact' in the navigation and the URL, but the page's header shows 'Contact me!'. With this change, the navigation item will still be bold if you are on the contact page.
  • .LinkTitle defaults to .Title if not set. I tested if .Name is equal to .Title, and this appeared to be the case (.Name is also unset if the title is not set). I also couldn't find anything about the .Name method in the Hugo documentation.
• The menu item's name is now also lowercased for comparison, so current page detection will also work for pages with an uppercase title.