added deputy to chair, added UI
Association between users and chairs for WiMis
added chair reference to user and vice-versa
Merge branch 'develop-ak-change-deputy' of https://github.com/tkowark/hpi-hiwi-portal into develop-ak-change-deputy

Conflicts:
	app/models/chair.rb
	db/schema.rb
integrated review comments
Merge pull request #85 from tkowark/develop-ak-change-deputy

added deputy to chair, added UI