#10

- implemented author method
#8

- added presence validation for :user_id, :rating and :content
#6

- added presence validation :title, :price and :description
- added format validation and numericality check to :price
#7

- added uniqueness and case sensitivity validation to :name
#9

- added user ownership and session state validation
Merge branch '#6'
Merge remote-tracking branch 'origin/#7'
Merge remote-tracking branch 'origin/#8'
Merge remote-tracking branch 'origin/#9'
Merge remote-tracking branch 'origin/#10'