changed session to singular resource
made MyFlix a link to home_path
fixed bug in average_rating

average_rating got a division error when there were no ratings.
added m:m relation for users video queue
added queue action to users_controller
added buttons to video show page
fixed links in header
adjusted routes for queue et. al.
wired up add to queue button
template for queue
add_to_queue controller
queue tests
a user can delete a video from her queue