Remove custom search viewlet since we won't use Google search.

Add articles-listing view which returns a custom sorted
list of plone.app.contentlisting contentlistingObjects:
3 featured articles, 3 normal articles, 1 featured article,
3 normal articles, continue alternating 3 normal: 1 featured
until no more featured.

Add Diazo rules to insert articles-listing template results
in the main column flow.

Diazo rule to add 'img-responsive' class to all img tags inside
of HTML article elements.

Make a METAL macro for article listing items which returns
appropriate HTML depending on whether it's featured or normal.