Admins can mark submissions as featured.

Featured submissions can be used to highlight solutions for
a particular challenge. An admin can select which submission
is a good example of how to solve a challenge and mark it as
"featured".
Prevent non-admins from featuring submissions.
Add foundation icons.

Will be used to indicate if a submission is featured or not.
Show featured submissions first.
Merge pull request #98 from atsheehan/featured_submissions

Featured submissions