Allowing to unsubscribe from DynDNS domains

[theo-is-taken]

The problem

If you happen to lose your DynDNS key, there's no way to reset the domain manually, and you must ask for support on the forum

The solution

You must now enter ( and remember ) a password when you register a domain. You can use it to later unregister the domain. I also added a warning if you try to unsubscribe from a DynDNS domain while having sub-domains of it.

Screens

PR status

We just need to wait until https://github.com/YunoHost/yunohost/pull/1472 is ready to merge