Issue #1497380 by Berdir, andypost, jibran, tim.plunkett: Convert shortcut sets to ConfigEntity.

core/modules/shortcut/config/shortcut.set.default.yml

...rtcut/lib/Drupal/shortcut/Plugin/Core/Entity/Shortcut.php

...s/shortcut/lib/Drupal/shortcut/ShortcutFormController.php

...s/shortcut/lib/Drupal/shortcut/ShortcutListController.php

...hortcut/lib/Drupal/shortcut/ShortcutStorageController.php

.../shortcut/lib/Drupal/shortcut/Tests/ShortcutLinksTest.php

...s/shortcut/lib/Drupal/shortcut/Tests/ShortcutSetsTest.php

...s/shortcut/lib/Drupal/shortcut/Tests/ShortcutTestBase.php

core/modules/shortcut/shortcut.admin.inc

core/modules/shortcut/shortcut.install

core/modules/shortcut/shortcut.module

core/profiles/standard/standard.install