Some modifications to the default configuration of log4j2:
1) added a comment to summarize the default configuration, with a reference to the online log4j2 documentation for further customizations
2) added a new appender for errors (or greater); implemented using a filter to keep the logger definition as clean as possible
3) removed the external appender because the amount of log statements (warnings or greater) from external jars is not large and should not cause much confusion if we keep them with OFBiz log statements
4) increased the number of rolling files for ofbiz.log to 10
5) changed date format to "yyyy-mm-dd hh:mm:ss.sss"


git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1633550 13f79535-47bb-0310-9956-ffa450edef68