Relationships

1) add view RelationshipsController specs
2) add Relationship model, specs
3) add validation on relationship to be unique
4) add user socializes spec - following, unfollowing

Please, approve.
Oh yes, this might be a little bit confusing because I am using should matchers, is it recommended to use expect(response) rather than https://github.com/thoughtbot/shoulda-matchers/blob/master/lib/shoulda/matchers/action_controller/redirect_to_matcher.rb?