Make has_one building syntax to look the same as for has_many

[Alex Galushka]

class User
  has_many :tips
  has_one :photo
end

user.tips.build(params)
user.photo.build(params)

Currently we have to use different syntax user.build_photo because user.photo can return nil. We can return some kind EmptyRecord instance the support the same methods that we have for has_many

user.photo.build
user.photo.create
user.photo.create!