Fixing remaining Spree 2.1 issues, a substantial increase in spec coverage

After my first pass at Spree 2.1 compatibility a number of issues remained, which were later exposed by additional specs.  This PR fixes those issues and adds a large number of specs to ensure against regression.

Key Changes:

1. Added missing permitted attribute for Spree::ReviewController
2. Fixed bug in FeedbackReview scope definition
3. Fixed bug in validation message in FeedbackReview
4. Fixed FeedbackReview controller so feedback reviews can actually be submitted.
5. Added stronger validation for Review
6. Added simplecov as an option for spec runs
7. Added database_cleaner to properly clean up database during spec runs
8. Moved request specs to standard 'feature' location
9. Added a FactoryGirl factory for FeedbackReview
10. Some minor refactoring of Review, including shifting the recalculate logic to Product in accord with Law of Demeter concerns
11. A very large increase in spec coverage, to ensure that the bulk of the code is tested.  Some additional specs on the controllers would be valuable, but the happy cases are essentially all tested.
12. Restricted advertised routes to supported routes