New changeRole action, allowed to superusers by default

[rrd108]

I understand you answer to issue #513 but why superuser can not edit the role of a user? should I really override the users controller for this basic need?

[steinkel]

I see what you mean, and I think it makes sense to add a specific changeRole action that is allowed by default for superusers. I'll change the title of this issue to keep track of this. Thank you