Added a feature allowing users can reorder videos in the queue.
Added a default scope to QueueItem for ordering by position ASC.
According the solution video, changing the way to sort queue items.
According the solution video, changing the route name.
According the solution video, adding a numericality validation to the position of the QueueItem.
According the solution video, changing the test spec of POST update_queue.
According the solution video, changing the queue items controller and it's test spec.
Normalized queue item positions after destroying one.
Moved codes from controller to model.
User can change video ratings in the queue.
Refactor codes by solution.
Moved the deuplicated position number test into user model.
Changed the way to iterate a hash.
Removed a useless variable.
Merge pull request #5 from HenrykChiu/week_3_code_review_1

Week 3 code review 1