Nav : display all navigations items and roles (or missing role)

[al2b]

For each nav :

• [x] Display name
• [ ] alert if there several navs with same name
• [x] display nav's name (aria-label)
• [ ] optional: display all links in each nav

<div id="main-nav" role="navigation" aria-label="Main">
  <!-- content -->
</div>

...

<nav id="footer-nav" aria-label="Footer">
  <!-- content -->
</nav>

<header>
  <nav id="main-nav" aria-label="Main">
    <!-- list of links to main website locations -->
  </nav>
</header>

...

<footer>
  <nav id="footer-nav" aria-label="Main">
    <!-- list of links to main website locations -->
  </nav>
</footer>