Add Preset for Student
[core] Rename student_id fields to *_code
Implement code for Student
Add Student code to index and show
[frontend] Add search by code to students index
[archive] Fix failing specs after field renames in Student
Mark as pending the student creation with class_group spec
Merge branch 'master' into student_id_number

Conflicts:
	archive/app/models/gaku/student_injector.rb
	sample/db/sample/gaku/changes/student_changes.rb