Add support for NonBlankString and StrippedString

[satorg]

Java 11 introduces new methods in String: isBlank and strip. Those methods complement good-old isEmpty and trim respectively but sometimes are way better suitable for processing locale-specific strings.

It should be fairly easy to capture this functionality in "refined" types like NonBlankString and StrippedString (that would complement NonEmptyString and TrimmedString respectively).