Add option «membership: none» to user edit view (fixes #54)

src/users/editUser.js

@@ -16,6 +16,11 @@ export default class UserEdit extends EditView {
       m(RadioGroup, {
         name: 'Membership',
         buttons: [
+          {
+            value: 'none',
+            label: 'No Member',
+            defaultChecked: this.data.membership === 'none',
+          },
           {
             value: 'regular',
             label: 'Regular AMIV Member',