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/filter_test.go

@@ -0,0 +1,37 @@
+package home
+
+import (
+	"net/http"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestFilters(t *testing.T) {
+	config.client = &http.Client{
+		Timeout: time.Minute * 5,
+	}
+
+	f := filter{
+		URL: "https://adguardteam.github.io/AdGuardSDNSFilter/Filters/filter.txt",
+	}
+
+	// download
+	ok, err := f.update()
+	assert.True(t, ok && err == nil)
+
+	// refresh
+	ok, err = f.update()
+	assert.True(t, !ok && err == nil)
+
+	err = f.save()
+	assert.True(t, err == nil)
+
+	err = f.load()
+	assert.True(t, err == nil)
+
+	f.unload()
+	os.Remove(f.Path())
+}