Whois domain: Query whois server to get domain information

This class is meant to query a whois server to retrieve information about a domain, specifically whether the domain is available for registration.

This class features:

- Domain name string validation

- Knows which whois server to query for domains of different top level domains (TLD).

- More TLD can be supported by adding the respective whois server entries in a separate configuration script.

- Generate an a form select input for the defined tld's.

- Simple domain avaialability check or full information query

- multiple domain query (for all tld's conf. with this class)