Migrate to letsencrypt wildcard certs

[uiharu]

Now that letsencrypt provides wildcard certs, cloudron should consider switching over to wildcard cert.

Benefits

1. No more hitting registration limits for users with a large number of apps.
2. Slight security improvement of not making app subdomains immediately public

[girish]

@uiharu We have implemented this now in our latest release. Should be out in the coming week or so.