Improve Shutdown Reliability - #213
* Give names to Monitor and Connection actors for easier tracking
* Add a Supervisor actor to MongoDriver that shutsdown the ActorSystem
* Make MongoDriver.close exit cleanly by waiting for ActorSystem to shutdown
* Make MongoDriver always use its own ActorSystem for increased isolation from other ActorSystems
* When MongoDBSystem is closing, if it gets a ChannelConnected, just close the channel and log a warning
* Add a test case to test the above.
* Replace LazyLogger with grizzled.slf4j.Logger for better support of logging (DRY).
* Don't depend on log4j just use slf4j-simple (fewer dependencies for upstream users of ReactiveMongo)
* Modernize the build infrastructure to sbt 0.13.6, add -feature to compiler so we can see language feature issues
* Various documentation fixes to quiet down warnings a bit.