Misleading actions in Users panel

[cortho]

While the guests app creates a virtual group from the group appconfig value, in the admin frontend it looks like a normal group. So it is possible to make an admin out of a guest and vice versa even when the backend does not support this.

[davitol]

Only webUI bug: It should not be possible to create a regular user and add it to a guest_group. (refreshing the browser we can see that the group is not set)