Url: Add new method getDomainWithoutWww().

[janbarasek]

• new feature
• BC break? no

Sometimes I want to get real pure domain always without www. prefix.

For example in the case of URL https://www.nette.org:

• method getDomain(3) return www.nette.org,
• but method getDomainWithoutWww() return nette.org only.