Article vote

Story ID https://www.youtube.com/watch?v=dul3OtLFBXI#t=459

Completed feature, however have not had a code review. Have attempted to keep article_vote feature in separate source files, which may not be desired, but segregated changes. Maybe too many cucumber tests and not enough rspec. Am issuing pull request, as well as adding Bryan Yap as committer on my branch to allow either pull to be merged or merging of upstream back to my branch.