Included log4j, revised code for classes

Update:
 - fixed doc strings for every methods and classes.
 - added method to read log4j.properties in REEFDriverDelegate.
 - removed doneWithSparkContextInit(),waitForSparkContextInit(), and acquiredSparkContext() 
Previous version had `sparkContextInitialized()` method which was used in REEFClusterScheduler to notify REEFDriverDelegate that SparkContext had been initialized. This method was removed, and I have not changed the doc string yet.