a property for reloading Labels when one desktop is created

feature spec

• support a property org.zkoss.util.label.reload

  <library-property>
      <name>org.zkoss.util.label.reload</name>
      <value>true</value>
  </library-property>
  

  Then ZK reloads zk-labels.properties when creating a new desktop (users reload a page)

• For the developement phase, users are modifying lable properties files, reloading can avoid them from restarting a server each time.
• it's the same idea like disabling a cache.

Note

after implemented, enable this in dev mode mentioned in ZK-4045

prototype

	private void enableDynamicLabelReloading() {
		try {
			WebApps.getCurrent().getConfiguration().addListener(LabelReloaderListener.class);
		} catch (Exception e) {
			logger.error("ZK-Springboot: Couldn't enabling LabelReloaderListener listener");
		}
	}

	public static class LabelReloaderListener implements DesktopInit {
		@Override
		public void init(Desktop desktop, Object o) throws Exception {
			Labels.reset();
		}
	}