Fixed exporter function in Users module

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| License       | MIT
| Doc PR        | -

Some details:

- Error is in module-Users, func-exporter when submit the form. The problem is in the template: it must post the *csrftoken*.

I have two questions:

- I don't know if I must add this little issues to *changelog* .
- Exporter function report a csv with groups names (like 'Users|Editors|Group A'). Import function needs groups *gid* (like '1|3|7'). Maybe it's better that exporter report *gid*s. It's not a bug... I can send a PR, but I'll wait your opinions.