*(querylog): added offset/limit parameters

Actually, this is a serious refactoring of the query log module. The
rest API part is refactored, it's now more clear how the search is
conducted. Split the logic into more files and added more tests.

Closes: https://github.com/AdguardTeam/AdGuardHome/issues/1559

util/helpers.go

@@ -10,6 +10,16 @@ import (
 	"strings"
 )
 
+// ContainsString checks if "v" is in the array "arr"
+func ContainsString(arr []string, v string) bool {
+	for _, i := range arr {
+		if i == v {
+			return true
+		}
+	}
+	return false
+}
+
 // fileExists returns TRUE if file exists
 func FileExists(fn string) bool {
 	_, err := os.Stat(fn)