Add the LogLevel OFF that can be used to turn off logging. See #2965

Conflicts:
	akka-actor/src/main/scala/akka/actor/ActorRefProvider.scala
	akka-docs/rst/java/logging.rst
	akka-docs/rst/scala/logging.rst
Change documentation to consistently use quotes for log levels. See #2965
Ensure that logging propagates since it is asynchronous. See #3069
Change event-handlers to loggers. See #2965
Only log log initializaton errors directly to StandardOutLogger. See #3069
Merge pull request #1173 from akka/wip-2965-show-how-to-stop-stdout-logging-master-ban

Add new log level OFF. See #2965