Configuration change listeners

Storagemanager components need to be able to change behavior on the fly to some extent. When the config file changes, the Config instance needs to notify the other components to update the config params that make sense. ex, it makes sense to be able to change the # of threads processing X on the fly, but it doesn't make sense to change the s3 bucket on the fly.

This ticket includes changes to Config, and changes to other classes to pick up & adapt to the new values.