changed look of custom variables screen, merge metadata when specified

core/DataTable/Row.php

plugins/CoreAdminHome/Menu.php

plugins/CustomVariables/Archiver.php

plugins/CustomVariables/CustomVariables.php

plugins/CustomVariables/Menu.php

...larjs/manage-custom-vars/manage-custom-vars.controller.js

...arjs/manage-custom-vars/manage-custom-vars.directive.html

...arjs/manage-custom-vars/manage-custom-vars.directive.less

.../angularjs/manage-custom-vars/manage-custom-vars.model.js

plugins/CustomVariables/lang/en.json

plugins/CustomVariables/tests/UI/CustomVariables_spec.js

...sts/UI/expected-ui-screenshots/CustomVariables_create.png

...sts/UI/expected-ui-screenshots/CustomVariables_manage.png

tests/PHPUnit/Unit/DataTable/RowTest.php