Add pairwise pseudonymous identifier support

app/controllers/api/openid_connect/discovery_controller.rb

app/controllers/api/openid_connect/user_info_controller.rb

app/models/api/openid_connect/id_token.rb

app/models/api/openid_connect/o_auth_application.rb

...ls/api/openid_connect/pairwise_pseudonymous_identifier.rb

app/models/user.rb

app/serializers/user_info_serializer.rb

db/migrate/20150613202109_create_o_auth_applications.rb

db/migrate/20150708154727_create_scope.rb

...0150801074555_create_pairwise_pseudonymous_identifiers.rb

db/schema.rb

features/step_definitions/auth_code_steps.rb

lib/account_deleter.rb

...controllers/api/openid_connect/clients_controller_spec.rb

...ntrollers/api/openid_connect/discovery_controller_spec.rb

spec/integration/api/user_info_controller_spec.rb

spec/lib/api/openid_connect/token_endpoint_spec.rb