Additional Enhancements to Challenge Submission

As a user, when I complete a challenge, I should be prompted to go to the next challenge (maybe make the "Next Challenge" button green).

As a user, when I view my previous submissions, I should see the code review for that solution.

Forgetting to submit a solution is kinda easy to forget. As a user, I should get a warning that my progress will be lost if I don't submit my code.