consistent function exports for Labels edit/new pages

app/assets/javascripts/pages/groups/activity/index.js

 import Activities from '~/activities';
-export default new Activities();
+export default () => new Activities();

app/assets/javascripts/pages/groups/labels/edit/index.js

 import Labels from '~/labels';
-export default new Labels();
+export default () => new Labels();

app/assets/javascripts/pages/groups/labels/new/index.js

 import Labels from '~/labels';
-export default new Labels();
+export default () => new Labels();