OSS E808 - Refactoring and Testing participant.rb, assignment_participant.rb, course_participant.rb 

This is the pull request for Expertiza project OSS E808 - Refactoring and Testing participant.rb, assignment_participant.rb, course_participant.rb . 

Nithya Pari - npari
Shilpa Mairpady - smairpa
Vineeta Khurana - vkhuran2