Add confirmation to enrollment model
Refactor mail receiver, add enrollment confirmation
Fix bug if it is course's first lesson
Add enrollment confirmation and welcome sender
Add lessons template
Add welcome email sender Sidekiq worker
Fix indents and styles
Add quiz sender worker, view and mailer
Move queue_next_quiz to Helper
Add TODO file
Add send_quiz view
Fix bug in SQL
Move some methods to welcome worker
Refactor helpers
Add Roadie gem
Refactor mailer and its workers
Show only confirmed enrollments
Use secret as ID for urls
Major refactoring
Modify and rename quiz#correct to quiz#result