restrict student user access to lectures and courses
student can't create new course and update devise test helpers
update login methods for controller specs
Courses edit contoller spec for students
Lecture controller spec student restrcitions
fix versions on comment for notebooks with no versions
student non-owners cannot delete a comment
teachers can delete student comments
notebook controller student/teacher permission to delete notebook
removed silly comments
Merge pull request #20 from instructure/user_restrictions

User restrictions for students and teachers