Issue #273 changing img to profile_image in student, TA, Lecturer

@ahmedhagii  @AhmedElassuty 
- changing img to profile_image in student, TA, Lecturer ....
- changing integer  "success" and "failure" to boolean  "success" and "failure" with a default of false 
- removing the uniqueness constrain on ids problem and student in attempts table
- adding relation has_many attempts in problem table