convert createLink to addDefinition
START PART 3: https://www.drupal.org/node/2301313
apply patch https://www.drupal.org/files/issues/menu-2256521-MenuLinkContentUI-review-do-not-test.patch
START PART 4: https://www.drupal.org/node/2301317
apply patch https://www.drupal.org/files/issues/menu-2256521-conversion-review-do-not-test.patch
and resolve 8.x conflicts
fix hook_uninstall to use the correct service
START PART 5: https://www.drupal.org/node/2301319
apply patch https://www.drupal.org/files/issues/menu-2256521-remove-dead-code.patch
and resolve conflicts with 8.x