OSGI Support

Issue #31 should be reopened as jar with metadata is not available in maven repo. PR of #31 added the profile to add that metadata, but this profile is getting executed. [Current (1.7) maven jar](https://oss.sonatype.org/service/local/artifact/maven/redirect?r=releases&g=net.logstash.log4j&a=jsonevent-layout&v=1.7&e=jar) does not contain required metadata.
