Allow modifying log levels of individual Play classes and packages

The current logging setup is an all or nothing approach where to change a log level for one class means you must change it for all classes, which is incredibly frustrating

Someone with Scala experience please check whether I am creating too many loggers. In Java I create them as static variables. In Scala there are classes, objects, traits, singletons, etc. that all have loggers. With the objects and singletons I believe I am only creating one total and not one per object instantiation. I have no idea with the traits though.
And, if you like, uses of `this.getClass()` in Scala can be just `this.getClass` without the empty parentheses.