Add a way to add appenders to loggers configured with @LoggerLevel

Loggers configured with help of @LoggerLevel in tests can now receive additional appenders. The resulting logger has additivity enabled and so the configured appenders are added to the existing one (the file appender that logs DEBUG logs and higher to target/trace.log and the console appender that logs WARN logs and higher to the console). For example, the following logger will print INFO logs to the console: @LoggerLevel(klass = DBSSession.class, level = "TRACE" , appenders = NuxeoLoggingConstants.APPENDER_CONSOLE_INFO) Thus, you will have slow DBS queries printed to the console.