PLF-4469 : Import ExtendedPropertyConfigurator class from platform-cloud (https://github.com/exoplatform/platform-cloud/blob/master/services/src/main/java/com/exoplatform/platform/container/ExtendedPropertyConfigurator.java) to allow to load additional configuration files (configuration.properties with default properties and exo.properties with user settings)
PLF-4469 : Customize ExtendedPropertyConfigurator to not let ContainerUtil.loadProperties display an error in logs if the file isn't found (${gatein.conf.dir}/exo.properties won't be provided by default)
PLF-4469 : Load user configuration from ${gatein.conf.dir}/exo.properties if it exists
PLF-4469 : configuration.properties must be loaded from classpath (platform-extension-config-VERSION.jar) to get default settings