Add an atom feed for cookbook versions to the cookbook show page
Merge pull request #234 from opscode/cookbook-versions-atom-feed

Cookbook versions atom feed
Make cookbook url validation stricter.

Use validate_url for Cookbook URL validations to ensure that no nonsense is
present.
Implement most downloaded/followed filters

Implement most downloaded/followed filters from cookbooks index. Also
add top three most downloaded/followed to cookbooks directory.
Merge pull request #245 from opscode/sort_by_downloaded_followed

Implement most downloaded/followed filters
Merge pull request #243 from opscode/strict_url_validations

Make cookbook url validation stricter.
Add category class to the cookbook partial.

This colors the cookbook partial based on their category.
Merge pull request #250 from opscode/cookbook_category_color

Add category class to the cookbook partial.
Add SMTP configuration to example .env
Add nokogiri as a dependency

Premailer requires nokogiri or hpricot as a dependency. It includes
neither as it lets the developer to decide which they prefer so we must
include one, I choose nokogiri.
Don't require raven

We should only require raven if a sentry url is provided which we're
doing in config/raven.rb. This removes it from being required by
bundler.