Moved log in method in concerns
modified:   app/controllers/application_controller.rb
new file:   app/controllers/concerns/authentication_concern.rb
modified:   app/controllers/homepage_controller.rb
modified:   app/controllers/session_controller.rb
modified:   app/controllers/talks_controller.rb
modified:   app/controllers/users_controller.rb
modified:   app/views/homepage/show.html.erb