fixed printing of default module when empty string is logged, closes #2357; added printf-style calls to log level classes, closes #1165; default log level changed from OF to empty string so explictly setting a module to an empty string works as expected aka no module
Merge remote-tracking branch 'upstream/develop' into develop
Merge pull request #2360 from danomatika/develop

ofLog: fix module print when given empty string & add printf style function to log level classes