Course sign up 2.6

Issue #164 

Reviewers:
@AhmedElassuty @ahmedhagii  @metawaa @Mamdou7 @AhmedOsam

The added files are:
- tutor/app/views/courses/sign_up.html.erb

The modified files are:
- tutor/app/controllers/courses_controller.rb
- tutor/config/routes.rb