feature--listing-header completed

[al-the-x]

Suggestions from class review in product.html:

• Reduce the amount of markup: simplify
• Use placeholders EVERYWHERE.
• Use data-src (or ng-src) with placeholders on images.
• Use dots instead of dashes inside of placeholders
• Try to map your placeholders to the API data, even if we don't have any yet...

            <nav class="featured-listings">
              <a href="{{listing.url}}" title="{{listing.title}}">
                <img data-src="{{listing.MainImage.url_75x75}}" src="//lorempixel.com/75/75/abstract">
              </a>
              <!-- TODO: Don't forget the "item count" box! -->
            </nav><!-- .featured-listings -->