Simplify Carbon Platform Logging Story

This pull request has introduced a way to plug user define logging providers. New log provideres should be inherited by LogProvider interface and configure it via logging-config.xml file. Because of export package confilict with logging component in kernel, all packages have been moved to "org.wso2.carbon.loggin.service" package. With the above package change it intorduce a change to log4j.properties file. CarbonMemoryAppender package has been changed.  I will send pull requests to fix that regression issue.