language settings for new attribute visibility
visibility array in student model
visibility id as permitted attribute in controller
visibility id in json files
visibility as view
visibility id concerned in ability
migration for visibility_id for students
rights for showing students
auto-generated schema.rb with new migration
Merge branch 'develop' into #380_Checkbox_for_student

Conflicts:
	app/controllers/students_controller.rb
	app/models/ability.rb
	app/models/student.rb
	db/schema.rb
erased merge problems
#380_Checkbox_for_students
corrected show for students and staff

#380_Checkbox_for_students
additional test case for invisible students
#380_Checkbox_for_students
Merge branch 'develop' into #380_Checkbox_for_student

Conflicts:
	db/schema.rb
Merge pull request #444 from hpi-swt2/#380_Checkbox_for_student

#380 checkbox for student