headteacher_define_manage_grades_test created
  - Defined Grade on top of test as let
  - Defined test_grade_should_save_grade method into test
  - Initialized headteacher_manage_grades_context
Grade model test and Grade model created
defined call method into headteacher_manage_grades_context.rb
Headteacher injected to person and created Headteacher module and its save method