DNSFilter: fix function declaration
Make Yandex and DNSFilter mutually exclusive, for simplicity (and since DNSFilter includes all of Yandex's functionality)
DNSFilter: implement default filtering support
DNSFilter: implement dnsfilter service action (for stop/starting)
Build: disable Yandex in favor of the new DNSFilter feature
DNSFilter: fix webui tabs
DNSFilter: Describe available services and provide links to provider's website on webui