Add pluggable logging for #426 v2

[agentgt]

See original issue. I'm of the high opinion that at least core configuration should not require logging otherwise you can't configure logging!!!

This change adds a private logging facade for archaius. I have set the default to NoOp but one could easily write a SLF4J and have it be the default. We could also use the ServiceLoader mechanism to load up a default logging implementation (I actually helped @mattrjacobs setup something similar for Hystrix plugins).

Of course the possibly simpler and perhaps better option is to not do any logging in archaius2-core and fail fast and configuration to ignore errors... etc.

Ignore the checked in pom file (I needed it because I'm mirroring in a corp environment with mercurial as a forked version and I can't edit the commit... yet). I will squash/edit the commit and remove it if there is interest in this addition.

[agentgt]

I figured out a simpler way that requires less code if you want to get the dependency to SLF4j:

package com.netflix.archaius.api.log;

import java.util.ServiceLoader;

import org.slf4j.ILoggerFactory;
import org.slf4j.Logger;
import org.slf4j.helpers.NOPLoggerFactory;

public interface LoggerService {
	
	public static class InternalLoggerFactory {

		/*
		 * Simply prefix Internal in front of LoggerFactory:
		 * So instead of:
		 * Logger logger = LoggerFactory.getLogger(MyClass.class);
		 * It should be:
		 * Logger logger = InternalLoggerFactory.getLogger(MyClass.class);
		 */
		public static Logger getLogger(Class<?> clazz) {
			return getILoggerFactory().getLogger(clazz.getName());
		}
		
		public static ILoggerFactory getILoggerFactory() {
			return LazyHolder.INSTANCE;
		}
		
	    //We should not load unless we are requested to. This avoids accidental initialization. @agentgt
	    //See https://en.wikipedia.org/wiki/Initialization-on-demand_holder_idiom
		private static class LazyHolder { 
			private static final ILoggerFactory INSTANCE = InternalLoggerFactory.createFactory();
		}
		
		private static ILoggerFactory createFactory() {
			/*
			 * You could also use a system property or static variable for resolution as well.
			 * The following looks for a file located here:
			 *  /META-INF/services/LoggerService.getPackage().getName()
			 * With the name of the class as a single line that implements LoggerService.
			 */
			ServiceLoader<LoggerService> loader = ServiceLoader.load(LoggerService.class);
			for (LoggerService ls : loader) {
				return ls.createLoggerFactory();
			}
			return new NOPLoggerFactory();
		}

	}
	
	public ILoggerFactory createLoggerFactory();

}