Fixed host adder dialog.
    
    The host adder dialog has been modified to show separate fields for
    hostname and DNS zone. The hostname is a text field and the DNS zone
    is an editable drop-down list. The fields will have the following
    behavior:
    
     - If the user types a dot into the hostname field, the cursor will
       automatically move into the DNS zone field.
     - If the user pastes an FQDN into the hostname field, the value will
       automatically be split into hostname and DNS zone.
     - If the user selects a value from the drop-down list, it will only
       change the DNS zone, not the hostname.
    
    Ticket #1457