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.
`is_expected` is syntax from RSpec 3.1 ? I am using 2.99 at this moment, I am not sure if I can use  new syntax yet. But yea well, I decided to go with 2.99 until the end of course at least :)

anyway there is small difference between the old should syntax and shoulda matcher.
old RSpec - ` response.should redirect_to xxx_url`
shoulda matchers - ` should redirect_to xxx_url`
I thought shoulda matcher would read better than expect(response) but I will with whether is better among developers :)