Issue #1616962 by fgm, rvilar, kalman.hosszu, fubhy: Replace ->title with ->label().

core/includes/form.inc

core/modules/book/book.admin.inc

core/modules/book/book.module

core/modules/book/book.pages.inc

core/modules/book/lib/Drupal/book/Tests/BookTest.php

core/modules/comment/comment.pages.inc

core/modules/comment/comment.tokens.inc

core/modules/forum/lib/Drupal/forum/Tests/ForumTest.php

...modules/locale/lib/Drupal/locale/Tests/LocalePathTest.php

core/modules/menu/lib/Drupal/menu/Tests/MenuTest.php

...odules/node/lib/Drupal/node/Tests/NodeAccessPagerTest.php

...es/node/lib/Drupal/node/Tests/NodeBlockFunctionalTest.php

...dules/node/lib/Drupal/node/Tests/NodeLoadMultipleTest.php

.../modules/node/lib/Drupal/node/Tests/NodeRevisionsTest.php

core/modules/node/lib/Drupal/node/Tests/NodeSaveTest.php

core/modules/node/lib/Drupal/node/Tests/NodeTitleTest.php

core/modules/node/node.admin.inc

core/modules/node/node.api.php

core/modules/node/node.module

core/modules/node/node.pages.inc