Models and Sign-in page added.
"Changed user.rb to match style guide."
New user model and role model.
Added abilities.rb, and role migrations
Role model, role migrations added
Abilities defined. CanCan Exception handling added
Users controller
Sign in and Sign up views
User model test suite
Teacher and Student models added.
Merge branch 'user-models-tony'

Conflicts:
	Gemfile
	Gemfile.lock