* reference logrus' global logger instead of passing and storing a logger reference everywhere
* always directly use global logrus logger instead of referencing an instance
* test suites should also directly use the global logrus logger
* rename gin logging function to clarify that it's middleware
* correct comments which erroneously referenced removed logger parameter
* setting log level for tests now uses logrus' exported type instead of the string value, to guarantee error isn't possible
tobi