Create group management UI
Please add some UI to list, add and remove so-called "Groups" in pages/shared/users/manage.vue.
Use this demo data in the view's data() function:
[
{ title: 'My Super Group', id: 'asdf-1234' },
{ title: 'My Other Group', id: 'qwer-5678' }
]Each group in the list has an edit button linking to the group's edit screen (see #380 (closed))