Supporting for multiple omniauth provider for the same user

app/controllers/omniauth_callbacks_controller.rb

app/helpers/profile_helper.rb

app/models/identity.rb

app/models/user.rb

app/services/notification_service.rb

app/views/admin/users/show.html.haml

app/views/devise/sessions/_oauth_providers.html.haml

db/migrate/20141121161704_add_identity_table.rb

db/schema.rb

features/steps/profile/profile.rb

lib/api/entities.rb

lib/api/users.rb

lib/gitlab/ldap/access.rb

lib/gitlab/ldap/user.rb

lib/gitlab/oauth/user.rb

spec/factories.rb

spec/lib/gitlab/ldap/user_spec.rb

spec/lib/gitlab/oauth/user_spec.rb

spec/models/user_spec.rb

spec/requests/api/users_spec.rb