Logger subsystems only support one logger name

When setting the "logger subsystems" you can only supply a single logger name in the code.
But, for example, to debug login issues, there are multiple loggers that needs to be set to a certain level, for example org.graylog2.security and org.apache.shiro.
Enhance the logger subsystem to support multiple packages, and adapt it accordingly for the existing subsystems so it makes more sense.