Merge branch 'topic/teacher' into topic/student

Conflicts:
	src/Due/EksamensBundle/Entity/School.php
	src/Due/EksamensBundle/Entity/User.php
	src/Due/EksamensBundle/Resources/config/services.yml
Merge branch 'topic/teacher' into topic/student
Created StudentInviteType.
Created service for StudentInviteType.
Created an action for inviting a student to the school.
Configured invitation form of students to be accessible only by the teachers of a current school.