Memory leak is possible

[artem-v]

Try run this artificial example:

    for(;;) {
      StringConfigProperty orderedProp1 = configRegistry.stringProperty("orderedProp1");
      orderedProp1.addValidator(s -> true);
      orderedProp1.addCallback((s, s2) -> System.out.println(s));
    }

Open jconsole and look at OldGen, it grows. The problem is at:

io.scalecube.config.AbstractConfigProperty#setPropertyCallback
io.scalecube.config.PropertyCallback#addConfigProperty