add convienience methods for log4j loggers

There is no concrete advantage that I know off. Just slightly more readable I would say if you use `def` since it will be more in line with the readers expectations. Not a big deal though.

Also if it was a `def` `RichLogger.logInfo(logger)` would be slightly more performant since it doesn't have to do the indirection through a separate class for the function. However, in your case this doesn't really matter.