Sort bookmarks by created_at DESC.

Sort bookmarks on index page so most recently created bookmarks appear first.

- Create seeds file to generate users and bookmarks.
- Setup FactoryGirl for testing
- Installed faker gem for FactoryGirl and seed.rb creation.

https://www.pivotaltracker.com/story/show/77836274
I see many people put factory_girl in with development as well. Honesty though, I am not sure why.