Merge branch 'blackst0ne/gitlab-ce-add_system_note_for_editing_issuable'

app/helpers/application_helper.rb

app/helpers/system_note_helper.rb

app/models/concerns/issuable.rb

app/models/note.rb

app/models/snippet.rb

app/models/system_note_metadata.rb

app/services/issuable_base_service.rb

app/services/system_note_service.rb

app/views/shared/notes/_note.html.haml

app/views/shared/snippets/_header.html.haml

...elogs/unreleased/add_system_note_for_editing_issuable.yml

...915_add_last_edited_at_and_last_edited_by_id_to_issues.rb

...last_edited_at_and_last_edited_by_id_to_merge_requests.rb

db/schema.rb

lib/gitlab/import_export/relation_factory.rb

spec/lib/gitlab/import_export/all_models.yml

spec/lib/gitlab/import_export/safe_model_attributes.yml

spec/services/issues/update_service_spec.rb

spec/services/merge_requests/update_service_spec.rb

spec/services/system_note_service_spec.rb