Refactor our handles() method to baseclass

This change removes the handle method, implemented in every service. It does this by moving up to the Service baseclass, and adding an attribute to the services instead (``supported_domains``). It is also more strict in that it will not accept a supported domain as a substring of the url as was earlier the case. The default handler will accept a domain listed in ``supported_domains`` or its www subdomain.

If any service is relying on the listed domain being a substring, please let me know before merging! I vaguely recall some service having country codes as subdomains, that should be added. Can't remember which one though.