Review urls structure

[gsouf]

• Think about a common interface instead of UrlArchive
• Review the relations between url/and urls that can generate requests (consider moving GoogleUrl::generateRequest away)
• Review the url factory (currently the constructor is used, that's not flexible)
• SerpUrlInterface should extend some UrlInterface

[gsouf]

The constructor was frozen for the factory. It's good because it allows url to remain a standard thing. If we need different way to construct url for search engines the best will be some special factories. For instance: Google::Url(...);