Allow specifying an arbitrary public name for the public virtual IP

This is important because end users can see a public FQDN (which can be
considered ugly) or this public name, but also because SSL certificates
need to be generated with valid names.

This is obviously HAProxy-specific.
Add sections to barclamp view to split settings more logically
Add a big info box about generated hostnames for virtual IPs

This is important to know when creating SSL certificates.