Added model for front-page news items

Addresses #567
Merge branch 'develop' into 567-editable_news
Added a field to toggle news is on homepage

Addresses #567
Wire up dynamic news on homepage

Instead of hard-coding news, use the new NewsItem model to display
news on the homepage.  Remove the hard-coded news items from the template
and their assets from the static directory.  The rendering of the
featured_news is accomplished through a new featured_news template tag.

Closes #567