filtering: refactor; change API; add "filters_update_interval" setting

+ config: "filters_update_interval"
* add /control/filtering_info
* remove /control/filtering/enable
* remove /control/filtering/disable

* add /control/filtering_config
* remove /control/filtering/status

* add /control/filtering/set_url
* remove /control/filtering/enable_url
* remove /control/filtering/disable_url

home/dns.go

@@ -49,6 +49,7 @@ func initDNSServer(baseDir string) {
 	config.dnsServer = dnsforward.NewServer(config.stats, config.queryLog)
 
 	initRDNS()
+	initFiltering()
 }
 
 func isRunning() bool {
@@ -165,6 +166,11 @@ func startDNSServer() error {
 		return errorx.Decorate(err, "Couldn't start forwarding DNS server")
 	}
 
+	if !config.filteringStarted {
+		config.filteringStarted = true
+		startRefreshFilters()
+	}
+
 	return nil
 }