Added Activities model. Activity added when Student is created. Activities are displayed. Corresponding styles added. Added Students on Navbar.

Files Modified

modified:   app/assets/stylesheets/bootstrap_and_overrides.css.scss
modified:   app/controllers/application_controller.rb
modified:   app/controllers/feed_controller.rb
modified:   app/controllers/students_controller.rb
modified:   app/helpers/application_helper.rb
new file:   app/models/activity.rb
modified:   app/models/student.rb
modified:   app/models/user.rb
modified:   app/views/feed/show.html.haml
modified:   app/views/layouts/application.html.haml
modified:   app/views/students/new.html.haml
modified:   app/views/students/show.html.haml
modified:   config/application.rb
modified:   config/mongoid.yml
modified:   spec/models/user_spec.rb