Issue #1800022 by Wim Leers, JohnAlbin, herom: Update Backbone and Underscore.

core/assets/vendor/backbone/backbone.js

core/assets/vendor/underscore/underscore.js

core/modules/ckeditor/js/ckeditor.admin.js

core/modules/contextual/js/contextual.js

core/modules/contextual/js/contextual.toolbar.js

core/modules/edit/edit.module

core/modules/edit/js/edit.js

core/modules/edit/js/models/BaseModel.js

core/modules/edit/js/models/EntityModel.js

core/modules/edit/js/models/FieldModel.js

core/modules/edit/js/views/AppView.js

core/modules/edit/js/views/ContextualLinkView.js

core/modules/edit/js/views/EditorView.js

core/modules/edit/js/views/EntityDecorationView.js

core/modules/edit/js/views/EntityToolbarView.js

core/modules/edit/js/views/FieldDecorationView.js

core/modules/edit/js/views/FieldToolbarView.js

core/modules/system/system.module

core/modules/toolbar/js/toolbar.js

core/modules/tour/js/tour.js