Improve code design after code review

app/controllers/profiles/chat_names_controller.rb

app/services/chat_names/find_user_service.rb

app/views/profiles/chat_names/index.html.haml

app/views/profiles/chat_names/new.html.haml

db/migrate/20161113184239_create_user_chat_names_table.rb

db/schema.rb

lib/gitlab/chat_name_token.rb

spec/lib/gitlab/chat_name_token_spec.rb

spec/services/chat_names/authorize_user_service_spec.rb

spec/services/chat_names/find_user_service_spec.rb

spec/support/matchers/be_url.rb