revert from part3 a form change that should be in part4
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
rename updateLink to updateDefinition
rename deleteLink to removeDefinition
rename isResetable() to isResettable()
convert topLevelOnly() to setTopLevelOnly()
fix destination
another destination fix
partial test fix
rename yml files
add back system block caching
don't eanble menu_link module per Alex
move SafeMarkup fix to part4
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