answers functionality
removed has variants functionality

added has_variants functionality

Changed db/schema.db for previous fixies

updated association for user
[Почему reference вместо foreign key](http://stackoverflow.com/questions/11535025/difference-between-foreign-key-constraint-and-references-in-rails)

Settuped association in survey factory

Settuped association in answer factory, deleted creating user_id, added belons_to :user
Added Variants functionality

Answer belongs_to user now, fixed association in factory girl

FIXED missing tests in spec/models

Fixed factories for answer and variants
RENAMED column  to  in Question because  is reserved for storing class in case of inheritance
Merge pull request #21 from tetianahogg/dev_parallel

Answers, variants functionality