Establish state of lesson progress [ "Not started", "In progress", "Finished"]
Modify layout of navigation swap Sign out for email
Use bootstrap class to style buttons
Use label method to set up progress of lesson
Use has many through association instead HABTM. Rename table from courses_lessons to lesson_completions. Add primary key and model for HMT association. Add new field for LessonCompletion, finished_at to check that user finished lesson