Allow many user ratings & reviews per user/movie

[lortza]

Currently, a user can add a rating and add a review to a movie they have seen. I would like to allow a user to add more than one of these items because opinions change over time.

I also think we could condense the rating and the review into 1 record, similar to any other product review we'd write. This new kind of review would have a review.rating and a review.comment (as well as the usual timestamps).

In order to migrate the existing data, my first thoughts are:

• if we trust that front end logic dictates possible data combinations, a user must have a movie screening for a review or a rating to be present, but a movie may or may not have either a rating or a review.
• add a new integer column on the reviews table that we'll call rating
• for each user, loop over all screenings
• next if the movie has neither rating nor review
• next if the movie has only a review (but log this somehow, maybe console putsing so we can see the data. we'll probably want to backfill it).
• if the movie has a rating and a review, copy the rating over to the review.rating field
• if the movie has only a rating, make a new review record, populating it with all of original rating data
• backfill any reviews that are missing a rating
• add null constraint to review.rating
• drop the old ratings table

Code changes:

• we have some queries like reviewed_movies and rated_movies that will require updating
• we can delegate the rating through the review if we want to
• front end changes are probably limited to the movie modal and show pages